A quarantine expansion has been declared following the detection of the citrus disease Huanglongbing (HLB), or citrus greening, in five residential citrus trees located in Rancho Cucamonga. This is the first time the disease has been confirmed in Ranch Cucamonga, marking the fifth city in San Bernardino County to have had a positive detection of HLB. The California Department of Food and Agriculture (CDFA) is working with the United States Department of Agriculture (USDA) and San Bernardino County to remove the HLB-infected tree and prevent the spread of HLB into neighboring areas.
The expanded quarantine area will merge with the existing quarantines in San Bernardino and Los Angeles Counties. The expanded portion is bordered on the north by Big Tree Cucamonga; on the west by Pauda Avenue in Claremont and Mount Baldy Road; on the east by Interstate 15; and on the south by Foothill Boulevard and Interstate 10 in San Bernardino County.
The updated HLB quarantine maps for San Bernardino and Los Angeles counties are available online. Please check this link for future quarantine expansions in these counties, should they occur.
The quarantine prohibits the movement of all plant parts or citrus nursery stock out of the quarantine area. Provisions exist to allow the movement of commercially cleaned and packed citrus fruit. If you are a grower within the new quarantine expansion area, please contact CDFA’s emergency quarantine response program at 916-654-0312 for information on these provisions.
Fruit that is not commercially cleaned and packed, including residential citrus, such as oranges, lemons, grapefruits and kumquats, must not be moved from the property on which it is grown, although it may be processed (removal of stems and leaves, and a thorough washing) and/or consumed on the premises.
Residents are urged to take several steps to help protect citrus trees:
Do not move citrus plants, leaves, or foliage into or out of the quarantine area or across state or international borders. Keep it local.
Cooperate with agricultural officials placing traps, inspecting trees, and treating for the pest.
If you no longer wish to care for your citrus tree, consider removing it so it does not become a host to the pest and disease.
CDFA staff have scheduled removal of the infected tree and are in the midst of a treatment program for citrus trees within 250-meters of the find site. By taking this action, a critical reservoir of the disease and its vectors will be removed, which is essential to protect other citrus trees on the property, neighbors’ trees and the community’s citrus from this deadly disease. CDFA, in partnership with USDA, local county agricultural commissioners and the citrus industry, continue to pursue a strategy of controlling the spread of the Asian citrus psyllids while researchers work to find a cure for HLB.
Questions? If you are a citrus grower in San Bernardino County and have questions about this detection, please contact your grower liaison Sandra Zwaal at szwaal2@gmail.com.
In 2020 the incidence of Pythium wilt (caused by Pythium uncinulatum) of lettuce has increased in severity and in the number of affected fields. Pythium infections in lettuce fields have been observed frequently, but not always, occurring with INSV infection. As a result, there has been confusion distinguishing between these two diseases and the role of each of them in causing the problems in fields. In this blog we will discuss these two diseases and explain from our current state of knowledge about the disease dynamics occurring in affected fields.
INSV has been a production problem on lettuce in the Salinas and surrounding valleys for a number of years and in 2020 it continues to be a serious production issue. Pythium wilt of lettuce is a relatively new problem and was first discussed in a blog entry in October 2015 by Steve Koike (https://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=19327 ). However, in 2019 and 2020 we have seen an increase in the number of acres affected by Pythium wilt as well as the severity within fields. Given that Pythium is a relatively new problem and the extent of the problem suddenly increased, some growers and PCAs are confronting this problem for the first time. To add to the confusion, at times INSV and Pythium infections are occurring together on the same plants which has caused confusion and has led to much speculation about the role of each disease in the observed damage.
Symptoms of INSV
Issues with INSV infections on head and leaf lettuce types are not a new occurrence in the Salinas Valley and many growers and PCAs are familiar with the symptoms and the patterns of infection in the field, especially on romaine. In general, INSV on lettuce causes characteristic patterns of chlorosis and necrosis on the inner leaves of the plant, as well as significant stunting (Photo 1). However, INSV can cause significant necrosis and lesions on and at the base of the ribs of lettuce plants (Photo 2). It should be mentioned that Tomato Bushy stunt virus (TBSV) can cause symptoms that can be confused with INSV and Pythium wilt; however, lettuce dieback symptoms are always seen on the outer, older leaves and the TBSV pathogen is commonly restricted to low-lying areas along the river. In addition, head lettuce varieties and some romaine varieties are resistant to this virus. When in doubt, it is important to have a sample tested. That said, INSV is the overwhelming virus issue facing growers and PCAs in 2020.
Moderate to severe symptoms of INSV on ribs of romaine.
Viral vs. Fungal Symptoms
One important detail about lettuce plants infected with only INSV is that they do not exhibit wilting of the outer leaves of the plant or show root rot or root discoloration. This is important to note because in 2019 and 2020 we have visited many fields where the plants exhibit symptoms of INSV and have wilting older leaves. In these situations, the roots and crowns of the plants should be examined for symptoms caused by soilborne pathogens such as the wilt pathogens (Fusarium and Verticillium), Sclerotinia, and Pythium. Fusarium and Verticillium do not cause rot on the fine roots or crown. However, they always cause characteristic vascular discoloration in the taproot and crown of the plant. Distinguishing these two pathogens without a laboratory evaluation is not advised, but in general, Fusarium occurs earlier in the crop cycle and often causes a red-to-brown discoloration internally along the taproot and at the base of the crown. Symptoms of Verticillium on the above ground parts of head lettuce become obvious close to harvest; the taproot and crown tissue of infected plants have dark brown-to-black discolorations. Plants with INSV can also be infected with Sclerotinia (S. minor) which is recognized by the characteristic rotting of the crown tissue of the plant and the presence of white, cottony growth and small blacksclerotia (Photo 3). Plants infected with Sclerotinia easily break off at the soil line when you gently tug on them. However, if the plants do not break off at the soil line and do not show any rot on the crown tissue but do exhibit rot on the fine feeder roots or lower down on the taproot, then Pythium wilt is suspected and can be verified by laboratory evaluation.
Sclerotinia infection on lettuce. Note that it infects and rots crown tissue of the plant.
Biology and Symptoms of Pythium
Pythium wilt is caused by the water mold, Pythiumuncinulatum. It infects lettuce roots with swimming spores (zoospores) that move to the roots within the water film in the soil. Additionally, it produces a second type of spore (oospore) that allows the pathogen to survive in the soil in the absence of a host plant. Previous studies have reported P. uncinulatum is almost exclusively a pathogen of lettuce and does not cause disease on other vegetable crops. However, it remains unknown whether other crops may contribute to a build-up of the pathogen in the soil. Affected plants will exhibit rotting of the fine and tap roots (Photo 4) and frequently dark discoloration of the inner core of the main root (Photo 5). Symptoms of the above ground parts of the plant include stunting, yellowing, and wilting of the outer leaves and eventual death (Photo 6). Sometimes the plants have a characteristic look where the younger leaves remain upright, but the older leaves are totally wilted down to the soil (Photo 7). This year, we frequently observed fields where plants are infected with Pythium wilt but are also infected with INSV. These mixed infections are confusing and make it more difficult to distinguish what is the cause of the damage. In our experience to date, plants that show foliar symptoms of INSV and that have wilting older leaves are typically infected with both INSV and, in many cases, Pythium wilt. It should be mentioned that we have also observed plants infected with INSV as well as Fusarium.
Pythium wilt infection of fine lettuce roots.Pythium wilt infection on lettuce taproot.Mini romaine infected with Pythium wilt.Romaine infected with INSV and Pythium wilt. Note that the older leaves are wilted and lay on the ground.
The distribution of Pythium wilt in a lettuce field can be variable. Earlier in the summer, fields with this disease typically were infected along the upper or lower ends of the field indicating that the disease may be responding to irrigation or drainage issues. It is possible that there may be a difference in the level of infection between sprinkler and drip irrigated fields, but we cannot say anything definitive at this time. The disease has been found from King City to Castroville. There is a significant difference in the susceptibility of varieties. In fields with multiple leaf type lettuce, we have observed significant differences in susceptibility among varieties with red types being less susceptible (Photo 8). Recently, there have been severe losses in some fields. It is not clear as of this writing, but it is possible that the incidences occurred in response to the heat spells. It is likely that diseased plants were not able to withstand the weather stress due to damaged roots or that extra water applied to address the heat may have stimulated the development of Pythium wilt. Another observation we have made is that at times Pythium mostly infects the fine roots higher up on the root system and in other situations it is more severe at the bottom of the taproot (Photo 9) which may indicate disease initiated farther down on the root system. Given that the disease needs a period of soil saturation for the swimming spores to travel to the roots, issues with soil preparation, drainage and irrigation management may affect the severity of the disease.
Difference in susceptibility of two green leaf lettuces and a green leaf and red leaf lettuce to Pythium.Plant with Pythium wilt infection lower down on the tap root (note the plant on the top with healthy fine roots higher up and infected tip of the tap root).
Research Efforts
Daniel Hasegawa is conducting research on the epidemiology and spread of thrips and INSV. JP Dundore Arias is working on a project with the California Leafy Greens Research Board monitoring the occurrence of Pythium wilt in the Salinas Valley. He is also characterizing isolates of this disease to better understand the organism and will be conducting preliminary evaluations of the sensitivity of the organism to fungicides. Given the rapid onset of severe damage of Pythium and the continued severity of INSV, we are trying to better understand these diseases and how they may interact. We are interested in receiving samples of Pythium wilt. Please contact Richard (rifsmith@ucdavis.edu) or JP (jdundorearias@csumb.edu) to submit samples.
Authors: Richard Smith, JP Dundore Arias, Daniel Hasegawa and Steve Koike
Farm Advisor, UCCE Monterey; Plant Pathology Professor, Cal State Monterey Bay; Research Entomologist, USDA ARS; Director, TriCal Diagnostics, respectively
A question came up about managing root-knot nematodes in processing tomato and lima bean rotations. Root-knot nematodes are tiny worm-like soil dwelling pests that cause root galling on plant roots, resulting in significant yield and quality losses. Symptoms of severe root-knot infestations include patches of chlorotic, stunted, necrotic, or wilted plants. These nematodes also predispose plants to other soilborne pathogens that cause root rot and wilt diseases. For example, a bean variety resistant to infection by the Fusarium wilt pathogen will become susceptible to this disease if infected with root-knot nematodes.
What is the link between nematodes in tomatoes and limas? Dr. Phil Roberts, Nematologist at UC Riverside shared the following response:
There are several root-knot nematode species and they differ in their response to resistance in tomato and various bean crops. Most common in our Sacramento Valley area are Meloidogyne incognita and M. javanica. These nematodes are normally controlled by Mi-1 gene based resistant tomatoes, but there are resistance-breaking populations so that could be the reason for the infection on tomato (unless the tomatoes grown were not actually resistant). A further possibility is that the species is M. hapla, which is not controlled by the tomato resistance. M. hapla tends to induce smaller pearl-like galls on tomato roots and is not common in the Sacramento and northern San Joaquin Valleys.
Root-knot Nematodes Causing Galling on Tomato Roots
As to rotating with lima beans, limas are susceptible to these root-knot species but there are resistant varieties available. Beja Flor baby lima has strong root-knot resistance. It was bred to contain three resistance genes that do a good job of blocking M. incognita and M. javanica. It yields well with the caveat that Steve Temple (former UCCE legume specialist) used to remark that it is more Lygus bug susceptible than some varieties, so if a grower went with UC Beja Flor they would need to keep up on the Lygus management. UC Luna baby lima has no root knot resistance. Other lines carrying M. incognita (but not M. javanica) resistance are the large limas White Ventura N and UC92.
If root-knot nematodes are present in a field with a history of Fusarium wilt, choose varieties that are resistant to root-knot nematodes as well as to the particular Fusarium wilt race present when possible. Another option is to rotate with root-knot nematode resistant cowpeas (blackeyes) instead of limas. Based on host-range tests, some varieties of cowpea have more root-knot nematode resistance than tomato. For example, some root-knot nematode races are virulent and highly pathogenic to Mi-1 gene based resistant tomatoes but not to nematode resistant cowpeas. — By Rachael Freeman Long & Amber Vinchensi-Vahl, UC Cooperative Extension
In what may be a first for science, researchers with the Agricultural Research Service (ARS) have found an example of plant and insect viruses working together to increase their spread.
Molecular biologist Michelle Heck, of the ARS Emerging Pests and Pathogens Research Lab in Ithaca, NY, scouts for aphids (Photo by Jennifer Wilson, Cornell University).
Michelle Heck, an ARS research molecular biologist, was leading research into poleroviruses, a type of plant virus spread by aphids, when she and Cornell University graduate students Jenny Wilson and Patricia Pinheiro made the surprising discovery. Heck is in ARS’s Emerging Pests and Pathogens Research Unit at the Boyce Thompson Institute, on the campus of Cornell University, in Ithaca, NY.
“Poleroviruses produce a molecule, called P Zero (P0), which dampens the aphid’s immune system,” Heck said. “When the aphid immune’s system is turned down, it allows an aphid virus called a densovirus to infect the insect at very high levels.”
Densoviruses have a curious effect on aphids: Aphids usually develop wings when the weather begins to cool, but densoviruses can induce the insects to sprout wings. When poleroviruses and densoviruses interact in this way, it allows them to carry the polerovirus farther and faster.
“We think this is the result of evolution,” Heck said. “Both the plant virus and the insect virus have evolved to manipulate the aphid. Our work shows they are in cahoots to promote virus spread, though possibly at the aphid’s expense.”
The research is vital to crop producers because aphids transmit more than 100 different viruses to peaches, tomatoes, potatoes, apples, cotton, cabbage, corn, and other plants. In particular, the potato leafroll virus can reduce the worldwide potato yield by more than 50 percent, causing the loss of 20 million tons of crop each year. There is a new and emerging polerovirus infecting cotton, cotton leafroll dwarf virus, that Heck and her team are now studying.
“Aphids are resistant to many commonly used insecticides, so chemical treatment is not effective in killing them and blocking the spread of viruses,” Heck said. “By the time a farmer notices aphids in the field, it is too late to block the spread of these viruses by aphids.”
Follow-on research includes a quest to understand how the polerovirus protein, P0, suppresses the aphid’s immune system at the molecular level. Heck is also looking at exactly how the densovirus triggers the aphid to grow wings.
“We now know that poleroviruses can interfere with the aphid’s immune response to densoviruses,” she said. The question Heck hopes to answer is, can the densovirus infection be made so severe that it kills the aphids, and if so, could it be used as a biological control tool? – By Scott Elliott, ARS Office of Communications
The false chinch bug (FCB), Nysius raphanus (Hemiptera: Lygaeidae), is a pest of many plants. FCB is a generalist and has been found to be a problem in many cropping systems such as soybeans, quinoa, tobacco, cotton, broccoli and other Brassicaceae plants. FCB adults (above) is mostly light to dark gray, elongate, and about 0.12 inch (3 mm) long. Females lay eggs on host plants or in cracks in soil. The mostly pale gray nymphs have inconspicuous reddish to brown abdominal markings. FCB has 4-7 generations per year with all stages being potentially present throughout the year. All stages can be present throughout the year. They also can be found invading homes in the southwest. Their populations generally start in unmanaged fields with lots of weeds and are an issue for crops when they build up large numbers and move into the crops from the unmanaged, weedy fields.
This year it’s host of choice is young avocado plantings in Ventura County. False chinch bug occasionally causes severe injury on young trees by sucking sap from shoots and young stems. Infested shoots wither and die suddenly after attack, which typically occurs in May and June. Economic damage normally occurs in groves away from the coast only on young trees in border rows adjacent to uncultivated areas or grasslands. Otherwise healthy mature trees tolerate bug feeding.
Here are photos of damage to young avocado provided by Tom Roberts, Integrated Consulting Entomology.
To best manage FCB, a grower will need to catch it before it establishes and the populations explode. This is difficult because the pest will not reoccur every year on regular basis. From what has been seen in the field this year, FCB appears to prefer young avocado plantings and thus, a targeted approach is to monitor only in new plantings right as summer temperatures are rising. In paper in the journal, Phytoparasitica from 2006, the authors investigated what color sticky trap was best for monitoring and found that yellow worked best. Thus, passive monitoring with yellow sticky cards that are placed throughout the field and monitored weekly is a potential option. However, this approach can be expensive with the labor hours needed to properly process the sticky cards. A more practical approach is to sweep net weedy areas on the outside of avocado groves and adjacent unmanaged areas nearby weekly in search for the first signs of FCB.
In conventional avocado production, there is only one insecticide recommended for use against FCB. Malathion 8 at 16 oz/acre.— By Monique Rivera & Ben Faber, UC Cooperative Extension
This is not good. You find an avocado tree with sun blotch or it is time to thin the orchard and you remove the offending tree. You know that if you don’t remove the sucker, you’ll end up with some rootstock growth that just gets in the way of the other trees. Avocado suckers can look like a valued tree until it’s time for harvest several years later, and then you are likely to find that it’s not the variety that you thought it was. Homeowners often find this problem several years after a freeze and the lemon tree that regrew from the freeze damage turns out to be the rootstock variety and produces some gnarly, seedy, juiceless fruit. Even without a frost, sometimes rootstocks which are selected for their vigor, can be more vigorous than the scion variety and will overgrow it. You then end up with whatever the rootstock fruit turns out to be.
In some situations, it is legal and common to use a “cut stump” treatment to kill stumps and prevent resprouting. In these cases, glyphosate or triclopyr is sprayed, drizzled, or painted onto a freshly cut stump. Relatively high concentrations of the herbicide are applied to the cambium, which is the living tissue just under the bark. Cut stump treatments work well in many situations, including citrus orchards. This type of cut and spray treatment is commonly done to remove undesirable plants, like arundo and weedy tree species. However, in some trees, like avocado and many forest species, there can be root grafting, which are tree-to-tree root connections.
Due to root grafting in a mature avocado orchard, it really can be one giant root system, one tree connected to all the other trees. And if a systemic herbicide is injected in one tree, the surrounding trees can be affected – they might get enough herbicide through the root graft to be injured or even killed along with the target tree. This technique has been used in Florida to remove Laurel Wilt Disease infected avocado trees which can rapidly infect surrounding trees with the killer fungus. This is a helpful technique, because it removes any doubt that all infected trees have been killed to prevent the spread to healthy trees in the orchard.
In a healthy orchard in California, this is not a really good way to remove avocado stump sprouts. Every year reports come in of glyphosate killing good trees that surround a removed tree. Figure 3 is a recent case where the stump (circled in blue) was scored and painted with glyphosate. Within two weeks the surrounding tree were also killed. The systemic material was translocated from the cut surface by way of root grafts to the neighboring trees. And those trees are now dead, too.
The stump (circled in blue) was scored and painted with glyphosate.
So what to do? One thing done by those with a front-end loader or a backhoe, is to pull the stump and have an end to the sucker problem. It also reduces the possibility of chronic armillaria fungus persisting to infect trees. The problem is that it leaves a big hole to deal with which can open up a slope to erosion. If on a slope, it requires a decent sized tractor that can safely be operated on the slope without tearing up everything, including the irrigation system. And in the end, it’s expensive.
The other approach is to just cut the tree down as low as possible without damaging the chain saw. Then as the irrigator makes inspections, just physically knock off the suckers as they come up. If walking the irrigation lines, it’s not a problem. Covering the stump and immediate area with a physical barrier such as thick, black plastic sheet (greater than 5 ml), can reduce the number of suckers. To speed degradation of the stump, the top of the cut can be scored and a salt such as urea or magnesium sulfate (both at 10 pounds per stump) can be applied. At this rate, rather than fertilize the stump, under moist conditions, this treatment facilitates the activity of wood-decaying microorganisms; it can also damage or reduce the regrowth of the suckers.
There are also a range of registered contact herbicides that can be used to burn out the suckers. Materials, such as Scythe®, Axxe® and Suppress® are all registered for avocado sucker control. There are others. These contact herbicide work best on small tender suckers so don’t let the suckers grow more than a foot or so. For best control of suckers, apply them at the highest allowable rate with an approved adjuvant at a spray-to-wet rate. Because these products are not systemic, you’ll likely need repeat applications, as new fresh buds break and new suckers erupt.
Using a contact spray means the grower would still need to be out in the orchard controlling the suckers. The grower still needs to be out in the orchard checking the irrigation lines. Why spray the suckers when they can just be broken off?
Although systemic herbicide can be used effectively to control suckers or stump sprouts in some tree crops or situations where root grafting does not occur, this is not a recommended practice for avocado because of the risk of damage to nearby trees. — By Ben Faber & Brad Hanson, UC Cooperative Extension
In late June, I was contacted by a watermelon grower and visited his field near the border of Stanislaus and Merced County. In the field, 50% of the plants showed leaf and vine wilt and about 20% died (see the field image). When I made a closer examination, the color of leaf lesions were chocolate brown and stem appeared to be watery (see leaf and crown images). The grower told me that the field was just harvested once but symptoms were already present beforehand. The field was planted by a 45-ct and mini-watermelon cultivars.
Vine-declined and wilted watermelon plants from the disease infection.
An initial suspicion was a fusarium disease and/or a possible Gummy Stem Blight caused by Didymella bryoniae, though this is very uncommon for the watermelon in California. I sent leaf, runner, and stem samples to the UC Davis Fungal Pathogen Lab and the results came back with the Fusarium Crown Rot caused by F. solani f. sp. cucurbitae and possibility of F. falciforme. F. falciforme has not been described to infect watermelon but records showed that it could cause crown rot in muskmelon. Gummy stem blight (Didymella bryoniae) colonies were not recovered from the samples, which did not surprise me because this disease is mostly prevalent in the southeast and north area, such as Georgia, South/North Carolina, and Delaware.
Unlike fusarium wilt caused by F. oxysporum f. sp. niveum, the vascular system of crown rot infected plants typically does not show discoloration far above soil line, instead, necrotic rot of crown and taproot can be seen. As the disease progresses, the rot on the crown develops from a light-colored, water-soaked area to be darker. Eventually, the entire plant wilts and dies. Evidence indicated that fusarium crown rot is more common on summer squash and pumpkin, however, all cucurbits can be infected.
Water-soaked, necrotic rot of the crown
Early planted fields can have a higher chance to be infected as disease is favorably developed under a cooler temperature. Soil moisture does affect the development of the disease. Extremely wet soil especially with drip tape breakage creates a favorable microclimate, which definitely accelerates the reproduction of spores and spread of the disease to other rows. Growers using surface drip irrigation should specifically pay more attention to the tape damage and fix the problem timely.
Various types of information demonstrate that the pathogen (F. solani f. sp. cucurbitae) is seedborne and survives only for two to three years in soil. A four-year rotation of planting non-cucurbit species is usually chosen for the disease control. In addition, choosing clean seeds or fungicide-treated seeds can reduce disease initiation. More information about the Fusarium crown rot on cucurbits can be found at UC IPM: http://ipm.ucanr.edu/PMG/r116100911.html. – By Zheng Wang, UCCE Vegetable Crops Farm Advisor
With almond and walnut harvest underway, it is a good time to review harvest nut sampling strategy and protocols for the best estimation of field loss by common pests. It is a general understanding that the grade sheet from your processers only represents about half of what is going on in the field. Also, the whole sum percent damage from the grade sheet does not identify which pest is causing the most economic loss. Insect population in orchards builds over time; therefore, knowing the history of damage helps to address potential risks and strategies to next year’s pest management program.
1. Harvest Sampling in Almonds
Taking a minimum of 500-1000 sample nuts from an average-sized orchard, anytime between shaking and sweeping, is recommended. Infestation can vary among different sides of the tree, and between edges and interiors of the orchard. This is especially true for navel orangeworm damage. Use paper bags to collect samples from multiple spots (>10 sampling spots, if possible) within the orchard. Store the sample bags in a cold room or freezer until you have time to do crack out. Look for damage signs associated with insect species described in the following paragraphs. Major insect pests for the damage evaluation are navel orangeworm (NOW), peach twig borer (PTB), oriental fruit moth (OFM), ants, leaffooted bugs (LFB), and brown marmorated stink bug (BMSB). BMSB is an invasive stink bug species, which is established and causing damage in almond orchards in the northern San Joaquin Valley.
1.1. Worm Damage (NOW, PTB, OFM). NOW feed in the kernel (nutmeat) and create deep feeding tunnels. Feeding by NOW results in a significant amount of white frass, and webbings on the kernel (Fig. 1a). Since NOW and PTB often infest the same nut, NOW feeding damage often masks the PTB damage. Feeding damage signs by PTB and OFM on the nutmeat are similar (i.e., the presence of the shallow tunnels and surface grooves on the kernels, and no webbings) (Fig 1b & 1c), except OFM leaves a small amount of reddish frass on the hull, which is absent in PTB damaged nuts.
Fig. 1. Almond kernels (nutmeat) damaged by: a) navel orangeworm, b) peach twig borer, c) Oriental fruit moth
1.2. Ant Damage. The percentage of almond damage by ants at harvest depends on the duration the nuts are on the ground after shaking. The longer almonds are left on the ground gives more time for ants to feed on them, results in more damage. Also, more damage is likely in orchards with drip or sprinkler irrigation compared to orchards with flood irrigation. Cover or vegetation in the orchards also favors ant activity. Nuts with tight shells or with narrower (<0.03-inch wide) hull split have less ant damage. Ants can completely hollow out the nutmeats and leave only thin skin (i.e., pellicle). Other signs of ant feeding damage include scraped or peeled pellicle and presence of “sawdust”, with the absence of webbings and frass (Fig 2a).
1.3. Leaffooted Bug and Brown Marmorated Stink Bug Damage. Most nuts infested by the leaffooted bug or BMSB, early in the season (mid- March to mid-May), abort and drop. A small percentage of those infested nuts do not drop but end up becoming shriveled and gummy kernels at harvest (Fig 2b). Both LFB and BMSB feeding after the shell hardening can result in sunken dark spots on kernels (Fig. 2c), although the degree of damage tends to be higher with BMSB feeding than LFB. Late-season feeding (July-August) by BMSB, can cause dark stained kernels (Fig 2d). Varieties with soft shells such as Fritz, Sonora, Aldrich, Livingston, Monterey, and Peerless are more susceptible to bug damage and for a longer period during the season.
Fig. 2. Almond kernels damaged by: a) ants, b-d) leaffooted bug and brown marmorated stink bug
2. Harvest Sampling in Walnuts
It is recommended to take a minimum of 1000 nuts at the harvest and evaluate for the damage caused by navel orangeworm , codling moth, ants, husk fly, and sunburn. It is important to have representative samples (>10 samples with a minimum of 100 nuts/sample) from the orchard for better estimation of the infestation. The damage signs associated with these specific insect pests and sunburn are described as follows:
2.1. Worm Damage (NOW, CM). Navel Orangeworm damage can be identified by the presence of a large amount of frass and webbings (Fig 3a). NOW larvae are present in groups and can bore deeply into the kernel. Heavy infestation may give a nutshell an oily appearance. In contrast to NOW, a single codling moth larva infest the nut, and has a lot cleaner damaged area inside the nut. Frass is evident, but only at the entry point on the husk; very little webbing present (Fig. 3b). If larva is present, look for crescent-shaped marking just behind the head to confirm navel orangeworm.
Fig. 3. Walnut damaged by: a) navel orangeworm, b) codling moth
2.2. Ant Damage. Similar to almonds, nut damage by ants increase as the duration of the harvested nuts on the ground increase. Ants enter the nuts from the soft tissues (i.e., stem end) and/ or through a codling moth injury. Ant damage on nuts is identified by the presence of deep chewing channels with clean kernels (i.e., no frass, no webbings, no deep boring) (Fig 4a).
Fig. 4. Walnut damaged by: a) ants; b) walnut husk fly; c) sunburnFig. 5. (Left) Brown Apical Necrosis is shown on the left, not to be confused with Walnut Blight, shown on the right, and caused by the bacterial pathogen, Xanthomonas arboricola pv. juglandis (Figure provided by Themis Michailides).
2.3. Husk Fly Damage. Walnut husk fly larvae (technical term: maggots) feed in groups by boring into the husk. Early season damage results in shriveling and darkening of the kernels, with the increased potential for mold growth. Late- season infestation causes little kernel damage (Fig. 4b), although it may stain the shell and make the husk removal process difficult.
Fig. 6. (Right) Moldy, off color nuts which lead to economic loss due to downgrading (Figure provided by Themis Michailides).
2.4. Sunburn Damage. Sunburn damage on nuts can be confused with husk fly damage. In the case of sunburn, nutmeat is shriveled and darkened on one side of the nut — no evidence of frass, webbings, or larval presence (Fig. 4c). Husks from sunburn damaged nuts can be removed from the shell during processing, which is not the case for the nuts damaged by husk fly.
— Article by Jhalendra Rijal, PhD, UCCE IPM Advisor, Stanislaus, Merced & San Joaquin Counties
Compounds produced by sorghum plants to defend against insect feeding could be isolated, synthesized and used as a targeted, nontoxic insect deterrent, according to researchers who studied plant-insect interactions that included field, greenhouse and laboratory components.
For this study, at the University’s Russell E. Larson Agricultural Research Center, researchers grew two nearly identical lines of sorghum — alike except that one, a mutant, did not possess the functional gene responsible for producing the flavonoids that essentially poison corn leaf aphids. Then researchers compared how the lines were faring.
The researchers examined the role of sorghum chemicals called flavonoids —specifically 3-deoxyflavonoid and 3-deoxyanthocyanidins — in providing resistance against the corn leaf aphid, a tiny blue-green insect that sucks sap from plants. To defend against pests like the aphids, sorghum has evolved defenses that includes biosynthesis of secondary metabolites, including flavonoids to poison the pests.
A previous Penn State study showed that in sorghum, accumulation of these flavonoids is regulated by a gene called yellow seed1 that controls responses to stresses such as fungal pathogens, noted Surinder Chopra, professor of maize genetics, Penn State. His research group in the College of Agricultural Sciences led both studies.
In the current research carried out at the University’s Russell E. Larson Agricultural Research Center, researchers grew two nearly identical lines of sorghum — one with a functional y1 gene that produced flavonoids, and the other a mutant called null y1, which did not possess the functional yellow seed1 gene responsible for producing the flavonoids.
The flavonoids are not present in the phloem — vascular tissue in plants that conducts the sugars aphids seek — but are in the epidermal cells that form the outermost layer of defense. When aphids repeatedly probe and puncture the epidermal cells with their stylets, or beaks, they take up the flavonoids that lead to their demise.
When they compared the two lines of plants, researchers found that a significantly higher number of adult corn-leaf aphids colonized null y1 plants compared to the plants with functional y1 gene that produced flavonoids. The aphids actively fed on the null y1 plants to where some of them showed signs of stress with yellowed leaves. The functional sorghum plants that produced the flavonoids had much lower aphid numbers and showed no ill effects from aphid feeding.
Greenhouse experiments with similar potted sorghum plants demonstrated that the aphids clearly preferred to feed and reproduce on null y1 plants, and the adults produced many more nymphs.
In a companion laboratory experiment, researchers fed two groups of adult aphids diets of sorghum leaf tissues — but to one they added an extract containing the flavonoids. After a few days, most of the aphids that fed on the flavonoid-enriched leaf tissue died and reproduction was curtailed — none of those aphids had nymphs before they succumbed.
On sorghum that didn’t have the functional gene to produce the flavonoids, researchers found that a significantly higher number of adult corn leaf aphids colonized on them and fed actively to the point that some of the plants showed signs of stress with yellowed leaves.
Perhaps surprisingly, Chopra explained, the flavonoids are not present in the phloem — vascular tissue in plants that conducts the sugars aphids seek — but are in the epidermal cells that form the outermost layer of defense. When aphids repeatedly probe and puncture the epidermal cells with their stylets, or beaks, they take up the flavonoids that lead to their demise.
The findings, published online in the Journal of Chemical Ecology, indicate flavonoids can potentially be deployed as potent insect deterrents to protect crops, Chopra suggested.
“Sorghum plants have evolved to precisely emit compounds offering defenses against harmful predatory insects that threaten them, and yet these chemicals in their defenses don’t hurt beneficial insects,” said Chopra. “If we could develop nontoxic insecticides, it would be a game changer — given that the toxicity of synthetic pesticides is of great concern, and they are considered to be dangerous to human health.”
Chopra, supported by Penn State, has applied for a patent on using flavonoids as insect deterrents. He pointed out that while much more research needs to be done, the most important consideration is that flavonoids are natural plant products that do not cause any pollution and are not harmful to human or animal health.
several varieties of Sorghum
This research may be an early step toward developing new phytochemicals for crop defenses, Chopra believes. “How well the flavonoids work against other herbivores is being researched, but we know with corn leaf aphids they are very, very potent,” he said.
Also involved in the research at Penn State were postdoctoral fellows Iffa Gaffoor and Sampurna Sattar, and Cullen Dixon, an undergraduate student, all in the Department of Plant Science; Nadia Frock and Juliet Moen, students in the Department of Entomology; and Associate Dean of Research Gary Thompson, professor of plant science. The team included Consuelo De Moraes and Mark Mescher, Department of Environmental System Science, ETH Zurich; and Rupesh Kariyat, Department of Biology, University of Texas Rio Grande Valley.
The research was supported by the U.S. Department of Agriculture’s National Institute of Food and Agriculture. — By Jeff Muhollem, Penn State University
California Department of Food and Agriculture (CDFA) Center for Analytical Chemistry (CAC) scientists Bahar Nakhjavan, Nighat Sami Ahmed, and Maryam Khosravifard were recently published in an academic journal after developing an improved method to test for mycotoxin in feed. Their article, “Development of an Improved Method of Sample Extraction and Quantitation of Multi-Mycotoxin in Feed by LC-MS/MS,” details their research of evaluating the three most popular sample preparation techniques for determination of mycotoxins, then selecting the best method and optimizing it.
Mycotoxins are the most common contaminants in agricultural crops produced by several species of mold and fungi. During growth, maturity, harvest, storage and processing of food and animal feed products, the fungus produces mycotoxins and other secondary metabolites. Mycotoxin-contaminated food and feed threaten human and animal health even at very low concentration.
Nakhjavan, Ahmed and Khosravifard work in CDFA’s CAC Environmental Safety Laboratory. Testing for mycotoxin in food and animal feed in the Regulatory Analysis Laboratory is part of their job of preventing contaminated food and feed from being consumed by humans, livestock and poultry in California. CAC uses state-of-the-art equipment and processes to test fruits, vegetables, nuts, animal feed, milk, water and air to ensure that pesticide and chemical levels are within the safety range established by national and international standards. Additional CAC staff who contributed to the work discussed in this published paper include Sally Henandez, Jose Salazar and Sarva Balachandra.
