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Pest Alerts, 7/1/2015
*This document has been edited for home gardening consideration.
Allium: White rot was diagnosed in garlic on one farm in Chittenden Co., VT. This fungal pathogen produces sclerotia that can survive up to 20 years in the soil without a host, making it very difficult to manage. The most effective way to avoid this disease is to plant seed from sources with no history of white rot into uninfested fields. Hot water treatment of garlic cloves at temperatures 115-118°F will greatly reduce the amount of pathogen present and is a good preventative measure, although it may not completely eradicate the fungus. Garlic germination will be inhibited above 120°F, so careful management of water temperatures is important. Leek moth larvae and damage continue to be reported in Chittenden Co., VT where this pest has become established over the last few years.
Basil: No new reports of basil downy mildew this week.
Brassica: Diamondback moth and imported cabbageworm were found at threshold on Brussels sprouts but not on collards in the same field and at the same growth stage in Washington Co., RI. Scout your brassicas separately as there may be host preferences for these crops. Untreated cabbage at the UMass research farm in Franklin Co., MA had sustained a lot of damage from ICW and large larvae were present.
Corn: European corn borer trap captures continue to be low to none in western MA and NH but have climbed in Chittenden Co. VT and Providence Co. RI to 7 this week. The field scouted in both RI and VT were below threshold. According to growing degree days, a second flight should occur soon: at 1400 GDD; first eggs 1450 GDD; and egg hatch 1550 GDD.. Corn earworm is being captured in central and south eastern MA at 3-5 moths per week, calling for a 5-6 day spray interval. Southwesterly storms this season has brought this pest into New England earlier than in the last several years. Fall armyworm traps in MA, VT and RI continue to capture 0 moths, and only one trap in NY reported a capture this week.
Cucurbit: Cucurbit downy mildew was reported this week on cucumber plants in Orleans and Allegany Cos., NY and in Berks Co., PA. Disease development is favored by just the sort of wet conditions and cool night-time temperatures we have seen quite a bit of so far this summer. Track the arrival and forecast risk of this migratory disease at: http://cdm.ipmpipe.org/. Current risk for CT, RI, Southern MA and Cape Cod is low and no risk in the rest of New England. Powdery Mildew was confirmed on Waltham butternut in Franklin Co., MA.
Striped cucumber beetle pressure was low in organically managed fields scouted in Hampshire Co., MA, Washington Co., RI, and Chittenden Co., VT. Squash vine borer trap captures have dropped into the teens in 25 out of 27 traps in NH, remain steady in MA and dramatically jumped in RI. Due to rain this week fields have not yet been scouted for eggs or larvae, and damage has not yet been reported by growers. In years with mild temperatures such as we are having this summer, SVB adults tend to remain active throughout the summer rather than dropping off in summer then returning again to infect fruit in late-August and September. Fields of bush type cucurbits with trap captures of 5 or greater and fields of vining crops with trap captures of 12 or greater should receive evening sprays targeted at base of the plant. Squash Bug adults but no eggs found in Chittenden Co., VT, and few adults and egg clusters found in fields scouted in NY, Hampshire Co., MA and Franklin Co., MA. No squash bug found at all in Washington County and Providence County, RI.
Solanaceous: Late Blight (Phytophthera infetans) was newly confirmed in Chittenden Co., VT, Wyoming Co., NY and Morris Co., NJ this week on potato. These recent samples have not yet been genotyped but US-23 was confirmed on potato in Livingston Co., NY last week. This strain affects both potato and tomato, so both crops should be considered at risk, and is sensitive to metalaxyl Early Blight was diagnosed on ‘Dusky’ eggplant in Chittenden Co., VT. This is the second diagnosis of this disease on this variety this year so the disease may have been seed borne. Use hot water seed treatment to prevent this disease on your crop next year. Bacterial leaf spot was confirmed on pepper in Chittenden Co., VT. This disease spreads quickly with rain splash and in humid weather. If seed-borne, it may start in one cultivar and spread to others. Three lined potato beetle larvae and adults were seen causing damage on tomatillo in Chittenden Co., VT. Eliminate nearby weeds in the solanaceous family, especially Physalis, also called husk tomato or groundcherry.
Multiple: Potato leafhopper was reported causing hopper burn in beans and strawberries in Washington Co., RI, on potato in Plymouth Co., MA, and on young apple trees in NH. Nymphs and adults have been seen in all locations. Plant later successions of beans away from the first successions, as this pest will continue to cause damage on younger successions next to infested crops. Also protect eggplants, as they are very attractive to PLH. Hopper burn on young snap bean plants is shown in photo below.
Weeds: Breakdown in weed control has been seen throughout New England with the high rainfall we have been receiving. Weeds such as crab grass can be very aggressive, especially in crops under 1 ft. tall. Cultivate if needed at this stage.