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University of Massachusetts Extension Vegetable Notes
Volume 16, Number 14 - August 4 , 2005 In This Issue:
Drought conditions in southeastern Massachusetts and southern Connecticut Valley are severe, with non-irrigated crops drying up and irrigation systems running full tilt where they are available. By contrast, upper CT Valley and some other regions received another inch or more of rain this week and losses to disease or excessive moisture were a problem in low-lying spots. In general, crops are growing fast and farmers are working hard to keep up with harvests. Peppers are coming in strong, and ripe tomatoes have reached ‘more than a trickle’ stage and will soon be a flood. Sweet corn is plentiful and of good quality. Flowering and fruit set on fall vine crops fluctuates with the heat; time will tell if yields are low this year as a result. Fall crops and late greens are in the ground but in some cases are suffering from heat or drought stress. Heat has exacerbated some problems such as bacterial leaf spot on pepper and internal tipburn of cabbage. Its time to plan for fall cover crops to sop up leftover nitrogen and prevent erosion over the winter. --R. Hazzard Cabbage looper has been observed in broccoli at the UMass Research Farm, which indicates that this migratory moth has arrived in the region though it does not tell where else it would be found or in what numbers. It does add to the assemblage of caterpillars that you need to scout for in brassicas. Look for the early feeding damage on the underside, which is similar with all three cateripillars: small holes that don’t go all the way through the leaf. Loopers are notable because of their ‘inchworm’ habit which can be seen even in early stages. They also are the biggest feeders of the three caterpillars. In daytime, the only adults you see are the cabbage butterflies. Diamondback and cabbage looper moths are only active a night. This makes it especially important to look under the leaves and find out what’s happening. --R. Hazzard Fall armyworm is showing up in pheromone traps and whorl-stage corn. Traps counts are generally low (except for a whopping 39 moths in Deerfield) but the presence of even one moth in a trap indicates that it is important to scout whorl stage corn. Flight trends tend to be more patchy than corn earworm; one farm might have it while another nearby farm does not. Damage in the field also tends to be very patchy, concentrated in adjacent plants together, probably the result of caterpillars from one egg mass spreading to nearby plants. Damage can be ragged and somewhat alarming (see photo) but its not unusual to find the damage done and the worm gone, having moved to the soil to pupate (as in photo). It is important to clean up FAW before the silk stage to prevent ugly damage from tunneling into the side or tip of the ear. Scout whorl or pretassel corn as you would for ECB and look for damage and worms. Feeding occurs inside the whorl leaves; small larvae can be found in the rolled-up whorl. Tassel damage and frass is more obvious than ECB. How do you know its FAW? Look for a smooth body, brownish color with lighter stipes, and a dark head capsule with an inverted Y in light tan or white. These caterpillars grow up to 1 ½ inches long. Check at least 50 plants in the field in groups of 5 or ten, to take a systematic sample for an accurate measure of the % plants infested. Combine the % with borer and % with FAW and spray if % infested exceeds 15%. Fields scouted this week were not over threshold yet, but should be checked as numbers of larvae may increase. European corn borer flight is still rising, and larvae from the second flight are starting to hatch. Scout pretassel and FAW feeding damage on tassel while still inside the whorl
green tassel corn. Where CEW is <2 per week, and ECB flight is over 7 per week, maintain a 6-7 day spray schedule on silking corn. Corn earworm remains remarkably low, especially for this time of year. Where captures are >3 or >7 per week, its time to move to a 5 or 4 day spray schedule (see chart). If you are maintining a pheromone trap for CEW, be sure to move it into fresh silk for the most sensitive measure of CEW activity. Moths are attracted to fresh silk. Try to rotate insecticides. Its tempting to use just one synthetic pyrethroid for all pests and all stages, but this is going to lead to resistance and poor control in the long run. Alternative chemistries are especially easy for the pre-silk stages. Try indoxycarb (Avaunt) which gives good control of FAW and ECB, or Spintor (Entrust) which is also good against both of these pests. In silking corn, Baythroid, Warrior, and Larvin are good for high pressure corn earworm situations; Spintor is good for ECB in silk and for low or moderate levels of CEW. Corn leaf aphids are present in corn, along with predators that can often, if not disturbed by sprays, keep them under reasonable control. Northern (like a green cucumber beetle) and western (spotted cuke beetle) corn rootworm may show up but are generally not damaging unless they reach high numbers. Organic growers who farm where CEW is traditionally a significant pest should be prepared for CEW arrival either with a good drop nozzle system, a good quantity of Entrust, and a plan for using the same spray schedule as conventional growers, or a Zealater with corn or soy oil mixed with Bt, spinosad or neem ready for a single application at 5-7 days after silk initiation. Studies conducted at UMass last year howed that spinosad gives equal or possibly better control, mixed with oil in the Zealator compared to Bt; and both corn and soy oil give equally good control with similar tip effects. Stollers Spray Oil with emulsifier may cause more tip injury than plain oil. The Zealater oil applicator is available from Johnny’s Selected Seeds in a new version that costs about $85.00. For a fact sheet on the oil method, consult the UMass Vegetable Program website. Or call the UMass Vegetable IPM office, 413-545-3696 and speak with Pam Westgate. SWEET CORN TRAP COUNTS 7-28 TO 8-4
--R.Hazzard, A.Duphily, B.Hunsdorfer, J.MussoniCORN EARWORM THRESHOLDS
Tipburn and internal browning are physiological disorders of similar origin. This condition is occurring in some FAW feeding damage on corn in whorl stage
fields of cabbage in the Connecticut Valley. Heads look perfect on the outside, but are unmarketable due to internal tipburn. Its seems that environmental and nutrient conditions worked together to cause the problem. This disorder, which also affects Brussels sprouts, Chinese cabbage and cauliflower. Since much of the state is suffering more from drought than excess moisture it may not occur in other regions; however, it is something to watch for due to high temperatures everywhere and uneven rainfall in many places. Symptoms The inner leaves of heads of cabbage and Brussels sprouts are affected, but there are no external symptoms. Margins of inner leaves turn brown, beginning at the hydathodes, and later desiccate to become thin and papery at the margin or over large portions of the leaf. The affected tissue may turn dark brown to black, occasionally being invaded by secondary bacteria that cause a watery soft rot. In cauliflower, internal leaves turn brown and fold over the developing curds. When secondary microorganisms attack these leaves, they become mushy, smear over the curd and make it unmarketable. Causal agent Tipburn and internal browning are caused by inadequate transport of calcium to rapidly growing tissues. Low levels of calcium at the leaf margin result in tissue collapse. The disorder can be caused by a lack of Ca in the soil, but usually results from the plant’s inability to move sufficient Ca to the young, actively growing inner head leaves at a critical point in their development. On a daily basis, Ca moves with the transpiration stream to the outside leafy parts of the plant that are actively transpiring on sunny days. At night, especially when dew forms, transpiration is reduced, and water movement generated by the roots is direct to the inner part of the head. However, on warm, dry nights the outer leaves continue to transpire and CA is diverted away from the head. Once Ca is fixed by the outer leaves, it cannot be translocated to the interior of the head. Environmental conditions that favor rapid plant growth favor tipburn. Abundant soil moisture promotes rapid growth, while excess moisture reduces soil oxygen levels, which in turn reduces calcium uptake and movement. Drought or root pruning also stress the root system and can impair the plant’s ability to take up Ca and translocate it to the young leaves at the center of the head. A warm dry spell after a period of abundant moisture may aggravate the disorder. Excess nitrogen results in large outer leaves that accumulate calcium at the expense of young expanding leaves within heads, and also encourages rapid growth. Wide spacing also encourages large outer leaves and rapid growth. Cruciferous crops grown on sandy soil are usually more prone to tipburn compared to plants grown on heavier textured soils. MANAGEMENT -Cultural Practices Factors that promote rapid plant growth should be avoided. Maintenance of optimum but not excessive fertility (including N) is important. Maintaining a phosphorous to potassium ratio of 1:1 should help to minimize the incidence of tipburn, because excess phosphorus can reduce calcium transport. Some of our soils have excessively high phosphorus relative to potassium. Irrigation may be necessary to maintain steady and optimum levels of soil moisture. Addition of high levels of calcium to the soil and foliar applications do not seem to alleviate the problem. Close plant spacing and prompt harvesting of crops when mature are beneficial practices. Internal symptoms grow worse as heads become larger and more mature. -Resistant cultivars Cultivars that grow less vigorously are less prone to this disorder. Resistant cultivars of Brussels sprouts and cabbage are available; check your seed suppliers for their recommendations. Growers are reporting that the culivars Internal tipburn in cabbage head
Cabbage tipburn
Note: head looks normal from outside Green Cup and Bronco had worse symptoms than other cultivars when the problem occurred in 2004 or 2005. It always impresses me that the disorders that are caused by lack of calcium in critical tissues – such as blossom end rot in tomato and tipburn of lettuce and internal tipburn of brassicas—are not really about lack of calcium in the soil, but about other factors that influence the availability and movement of Ca into the tissues. --Compiled by R. Hazzard. Sources: Howard, R.J., J. A. Garland, and W. L. Seaman. Diseases and Pests of Vegetable Crops in Canada, Canadian Phytopathological Society and the Entomological Society of Canada; Nonpathogenic Disorders of Cabbage, Robert Becker, Cornell Cooperative Extension Fact Sheet; A Sherf and A. Macnab, Vegetable Diseases and their Control. EGGPLANT AND POTATO: COLORADO POTATO BEETLE RISES AGAIN The summer generation of Colorado Potato Beetle adults have been emerging (look for round holes in the ground where they came out from the soil, where the pupal stage hides out). Those that emerge before August 1 lay eggs and produce a second flush of larvae. Those that emerge after August 1 don’t lay eggs. All of the adults feed rather heavily, in eggplant and potato. After about August 15, CPB adults begin to leave the fields and move to field borders where they will overwinter. Beetle eggs hatch quickly in the heat, and larvae feed and grow quickly. Try to control them before they are 2/3 grown; it is the final instar that does 85% of the feeding damage. If potatoes are in the tuber bulking stage, they can tolerate quite a bit of feeding damage (>20%). Don’t try to kill every beetle in the field. Food reserves in the foliage two weeks prior to senescence add little to final tuber bulking. Beetle adults can be particularly damaging in eggplant, where they clip flower buds aas well as feeding on leaves. Scout for adults, eggs and larvae to determine which stages are in your crop and at what density. For resistance management, given the famed and truly remarkable capability of CPB to develop resistance, it is critical to rotate among classes of insecticides. The most effective way to extend the useful life of an effective product is to use it on a single pest generation only, and then on the next generation, use a second pesticide with a different method of killing the pest (mode of action). For example, if you used Admire or Platinum as a furrow drench or Provado or Actara as a foliar spray on the first generation, DO NOT use them on the second generation. The neonicotinoid group should be used only once per season (and not at all if resistance has developed from continuous use). That includes the soil treatments as well as foliar treatments. These can be confusing because soil-applied and foliar insecticides with the same active ingredient have different names – as do the seed treatments. See Table 1. Table 1. Common Neonicotinoid Insecticides Registered for Vegetable Crops
Use alternatives to insecticides that no longer work well as a result of resistance, or to insecticides that DO work well, if you want to keep them working! Classes (different modes of action) include: -Synthetic pyrethroid (Asana, Pounce, Baythroid or Ambush) Many CPB populations are already resistant to these; if used, include PBO. Not as effective at high temperatures. -Carbamates (Thionex, Vydate); -Neonicotinoids (Admire, Platinum, Actara, Provado); -Spinosad, (Spintor, Entrust); -Bacillus thuringiensis (Novodor), -Abamectin (Agri-Mek, Abba 1.5 EC). AgriMek, Spintor/Entrust and Novodor all can be used effectively as alternatives to neonicotinoids, carbamates and pyrethroids. One low-risk strategy would be to use a material such as spinosad, which control adults and larvae for the first spray, followed by a Bt to kill emerging young larvae or Agrimek to control all stages of larvae. These three insecticides each have a different mode of action. They have not shown field resistance in this area (yet) and provide good options for alternate insecticides that provide effective control: Spinosad (SpinTor 2SC, a liquid formulation or Entrust, an organic formulation, dry powder) gives excellent control of all stages of CPB at the 3.5 to 4.5 fl oz rate. Spintor has the advantage that it will control adult CPB and also European corn borer if a grower has that pest on potatoes. It is currently the only effective CPB insecticide approved for organic growers. It can also be used on brassica and sweet corn pests. Labeled for fruiting vegetables as well as potato. Abamectin (AgriMek 0.15EC) is a selective insecticide for Colorado potato beetle on tomato and potato or mites and leafminers on cucurbits, peppers and tomatoes. Also for leafminers on head lettuce and spinach. It is derived from a metabolite of a soil bacterium, Streptomyces aver mitilis . It is mainly a contact material, which controls all larval stages. It is more effective against larvae than adults. It may be best used early in the season, when good coverage is easier to obtain. However, if you are battling resistant populations, it is worth using. Rates of 5-6 fl oz rate per acre gave effective control in commercial fields in trials on Long Island. The lowest labeled rate is 8 fl oz. Agrimek is labeled for potato and tomato, but not for eggplant. Bt tenbrionis (Novodor FC) controls small larvae, through the third instar. Time applications to begin when 30 percent of the eggs have hatched, or when larvae are no bigger than third instar (about 2/3 grown) as it does not work well against the large grubs. Where fields are densely populated and eggs are hatching continuously, reapply every 5 to 7 days. Currently there are no formulations of Bt tenebrionis products that are approved for organic use under the National Organic Program. You can check with the MASS organic certification program (MICI, 978-297-3644) for more details. Labeled for fruiting vegetables as well as potato. --R. Hazzard TWO SPOTTED SPIDER MITES IN TOMATO AND EGGPLANT Two spotted spider mite outbreaks have been reported in several mid-Atlantic states on many crops, including field and vegetable crops. These pests are generally associated with hot, dry weather, and we have had plenty of that with more to come! Check eggplant, tomato, cucurbit, bean, pepper fields and others at least weekly to spot spider mite problem areas. Concentrate on border areas, or field edges near hedgerows, or vegetable fields bordered by field crops such as soybeans. Look for the early signs of damage: white stippling at the bases of the leaves, whole areas of the field looking off-color, followed by yellowing of the leaves, webbing, and eventually defoliation. If the plants look off-color, look closely on the leaf undersides to determine if mites are the reason. Once webbing begins, it is difficult to control spider mites. Many different products are now effective and labeled for spider mites in vegetables, including Acramite, AgriMek, bifenthrin, Danitol, dimethoate, Kelthane, MSR, Vendex, Vydate. Check label for crop listings (also refer to updated New England Vegetable Management Guide at www.nevegetable.org), and obtain thorough coverage of the plant for effective control. Do not wait until the population is high, leaves curl, turn yellow or brown, or webbing begins as control will be reduced or not achieved at all. Target sprays for adequate coverage of the foliage to the leaf undersides – use drop nozzles, or high pressure sprayer. Begin checking your fields now. --Adapted from Gerald M. Ghidiu, Ph.D., Specialist in Vegetable Entomology. Rutgers Plant and Pest Advisory, 8-3-05 NO CUCURBIT DOWNY MILDEW HAS BEEN REPORTED in New York or New England to date. The closest reported outbreak is in southern New Jersey, and the downy mildew forecasting website rates the risk of new infections in this region as low. This is good news for all cucurbit crops and growers. Spray schedules and choices can be driven by powdery mildew, which is widespread now and showing up in pumpkins as well as other vine crops. Given dry conditions in much of the state, spray intervals can be extended to 10-14 days. This is especially true where a systemic such as Nova or Pristine is used. Combine with a protectant such as chlorthalonil or sulfur as a resistance management strategy as well as to expand the range of diseases controlled. Scout your fields looking on the underside or top of the leaves (especially older leaves) for small round spots of white spores. Once you find PM, this initiates your control sprays. Also, scouting will mean that you find downy mildew early, if it does come in to the region. Look for many small, half inch or smaller sized angular dark spots on the leaf. Fortunately, this is a disease that can be controlled easily if spotted in time. You will have probably 4-5 days from when you see the disease to when the vines collapse. This should give you time to make an application. Out TSSM and eggs
TSSM feeding damage on eggplant 
breaks can be very localized. So scout your fields! If you suspect downy mildew, call the UMass Disease Diagnostic Clinic at 413-545-1045 or 413-577-1827. Nova or Pristine work best when initatied at an early stage of PM, when it is first observed. Start with one of these plus a protectant, then the other 10-14 days later, also with a protectant. If other diseases like downy mildew should occur, then specific materials need to be incorporated into the spray schedule (ie. Acrobat, Curzate, Gavel, Previcur Flex). Note that while strobilurins ( Flint, Quadris, Cabrio) are not effective against powdery mildew because of resistance, they are still considered good choices for control of Plectosporium and some other diseases. Phytophthora blight may show up after thunderstorms where parts of filed are flooded, or if irrigation systems have leaks that keep low spots soggy for long periods. If you have crops in areas of flooding, it is probably better to pull those plants up now and not risk an outbreak of phytophthora blight in the field. Disk a clear a buffer area around wet spots with no plants so the rest of the field will be protected. New symptoms of bacterial wilt may still be showing up in vine crops. The disease is transmitted by striped cucumber beetle, generally when plants are small, but symptoms may not develop until several weeks after feeding damage was done. Crop and cultivar difference in susceptibility can be dramatic. The disease is not transmitted from one crop to another except via cucumber beetle feeding on leaves or stems. Spotted cucumber beetle (also known as western corn rootworm) can also transmit bacterial wilt. Squash bugs, if numbers are very high, can also produce wilt symptoms in vine crops. See earlier article (June 30 issue) for more details. -R. Hazzard. Adapted from Tom Zitter and John Mischanec, Cornell Cooperative Extension. TOMATO: BACTERIAL CANKER REPORT FROM EASTERN NEW YORK Bacterial canker is showing up in a lot of fields. You will first see dry, dark brown spots along the edges of the leaves, “marginal scorch”. You will also see the very symptomatic spots on the fruit. Spots will be small, the size of the pin head with a white halo around the spot. Early blight looks somewhat similar with brownish bronze colored lesions on the leaf but you will not find spots on the fruit with early blight. In most of the fields I have seen, the problem is spread out through out the entire planting. This very likely means the problem occurred in the greenhouse. Tomato transplants are most susceptible to the spread of bacterial problems when they are in the greenhouse. The plants are grouped together in a tray and watering will easily spread the problem from plant to plant quickly. Symptoms do not show up right away. Often if there is trickle irrigation, the plants will grow fairly well till a heavy fruit load and hot weather start to stress out the plant. That’s when you will most often start to see symptoms. I have seen growers save a crop with frequent copper sprays, good coverage, and high rates. Copper plus mancozeb is the recommendation for conventional growers until harvest; once harvest begins, the 5-days-to-harvest interval makes it difficult to use mancozeb. Copper can be used by organic growers, but note that many of the copper materials are prohibited for organic. One that is allowed (actually it has ‘regulated’ status) in MA is Champion WP. Check with your certifier! While sprays for early blight can be extended to 10 days to two weeks, copper sprays for bacterial canker need to be applied weekly. Copper washes off easily in a rainstorm. Do not use an airblast sprayer to apply copper; it will spread the bacteria across the planting. On plants with heavy fruit loads, we are beginning to see a lot of early blight. You will see bronze colored spots on the lower leaves. Look for concentric circles inside the spots. There are confirmed reports of late blight on tomatoes in southern Pennsylvania and in potato in northern Maine. With the dry conditions, it is not expected to cause a wide spread problem but it is a good idea to have some fungicide or copper protection on your tomatoes. -Adapted from John Mishanec, eastern NY Pest Alert. Vegetable Notes, Ruth Hazzard, editor and Ben Hunsdorfer, Assistant Editor. Vegetable Notes is published weekly from May to September and at intervals during the off-season, and includes contributions from the faculty and staff of the UMass Extension Vegetable Program, other universities and USDA agencies, growers, and private IPM consultants. Authors of articles are noted; author and photographer is R. Hazzard if none is cited. Where trade names or commercial products are used, no company or product endorsement is implied or intended. Always read the label before using any pesticide. The label is the legal document for product use. Disregard any information in this newsletter if it is in conflict with the label.
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