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Pest Alerts for Vegetable Growers: May 21, 2015

May 21, 2015

Scouting data for Pest Alerts is being collected regionally this year, from farms in Rhode Island, Vermont, and Massachusetts thanks to funding from the Northeastern IPM Center. Additional reports come from Extension Educators who scout on farms in NY and NH. When not given here, refer to the New England Vegetable Management Guide for scouting thresholds and treatment options.

Allium: Onion maggot flies have emerged, but have not reached peak flight in any of the locations in Table 1. Yellow sticky card traps placed in a field in Worcester Co. MA captured only 5 adults over the last 2 weeks. Onion fields were scouted in the following counties and no eggs were found: Chittenden, VT; Franklin, Hampshire and Worcester, MA; and Washington, RI. Place yellow sticky cards in fields now to monitor peak flight at 700 GDD (base 40° F) then scout for eggs and maggots by scratching gently around the plant roots with a pencil. Preventative soil insecticide applications are recommended for the control of first generation larvae if damage from the previous year’s crop exceeds 5 to 10%. Monitoring now will help to determine if preventive treatments, including use of row covers, are warranted in future seasons.


Cabbage Maggot: All locations reported in Table 1 have exceeded peak flight of the overwintering generation. Flies were captured on yellow sticky cards in brassica fields in Franklin Co, MA and Worcester Co, MA.  Eggs were scouted above threshold (average of 1 egg per 25 plants scouted) in cabbage, bok choy and kale fields in Franklin and Hampshire Co, MA (5eggs per plant). In the warmer conditions of a greenhouse, maggots have been reported in broccoli transplant trays causing damage. A new material (Verimark) is available for transplant and field drench applications and has systemic activity. In trials conducted at UMass in 2014, this material provided excellent control. In the field, floating row covers provide an effective barrier against this pest provided the adults are not emerging from overwintering pupae in soil that had brassicas last year. Avoid damage by planting after first flight is over, or 700 accumulated GDD’s (base 40°F). Drought conditions now may cause transplants to look like they have maggot damage, so be sure to scout for eggs before making any treatments.

Table 1. Accumulated Growing Degree Days (Base 40°F) and % emergence as of 5/20/15 for Cabbage and Onion Root Maggot. Values based on NEWA Maggot models.
Location Accumulated GDD’s (40° F) Cabbage Maggot Emergence y Onion Maggot Flight Peak z
Ashfield, MA 591 78% < 1st Peak
Waltham, MA 660 90% < 1st Peak
Seekonk, MA 695 95% < 1st Peak
Middletown, RI 615 82% < 1st Peak
Burlington, VT 647 88% < 1st Peak

Adult emergence from overwintering pupa:

y Cabbage Root Maggot 1st emergence = 288 GDD, 25% = 366 GDD, 50% (Peak) = 452 GDD, 95% = 687 GDD

z Onion Root Maggot 50% emergence (Peak) = 700 GDD

Flea Beetle: Both striped and crucifer flea beetles have been observed causing injury to young cabbage seedlings in in Franklin Co., MA, on multiple brassicas in Washington Co., RI and on greenhouse pak choi in Chittenden Co., VT. While they have a preference for non-waxy Brassica rapa species such as pak choi and arugula, even the waxy brassicas are susceptible to this pest, especially early in their growth. Spunbonded row covers provide excellent protection if well sealed at the edges. Rotate spring crops as far as possible from last season’s fall brassica crops and try to locate fall plantings as far from early successions as possible. A working threshold of 1 beetle per plant or >10% average leaf damage on 50% of the plants has proved effective in leafy greens and early stages of heading brassicas. See article this issue for more on managing flea beetle.

Sweet Corn: Pheromone traps have been set up at 25 locations in New York state, and one European corn borer E strain (NY) was captured in Ontario Co., NY.  You know what that means?  Set out your corn traps, especially for sweet corn started under plastic, and order Trichogramma! Releasing Trichogramma ostriniae, the tiny wasp that parasitizes the eggs of European corn borer, can reduce or eliminate the need for pesticide sprays to control this pest. To ensure that you will be able to receive Trichogramma this year you must call IPM labs as soon as possible. The wasps are custom-reared based on pre-orders, so let IPM labs know your needs well in advance. When placing your order, have the number of acres in which you plan to release and the size and number of plantings you have for early corn. Trichogramma can also be ordered for later-season releases to control second generation ECB in sweet corn and fruiting bell peppers. Trichogramma ostriniae can be ordered from IPM Laboratories; Locke, New York; 315-497-2063;

Chard and Spinach: Leaf miner eggs and maggots were found in Washington Co., RI, Bristol Co., MA, and Hampshire Co., MA. Scout your fields now by inspecting the undersides of leaves and treat when egg masses are observed, in order to target them before they hatch. Be sure to adjust spray nozzles to access the undersides of leaves as that is where the eggs are found, and add a spreader/sticker to the mixture in order to get better coverage. Avoid planting spring crops near tunnels where winter spinach was grown. Control weed hosts including lambsquarters, nightshades, chickweeds and plantains. Row covers protect the crop by excluding flies, but scout for eggs on transplants before covering. Some systemic insecticides are registered that may be applied to transplants or to the soil. Among organic products, spinosad has demonstrated efficacy when applied before egg hatch.

Cucurbits: Striped cucumber beetle has not yet be observed, but preventive actions can be taken now, as the adults will be emerging soon from field edges and your young seedlings will be at risk. Spunbonded row covers exclude beetles: use hoops to prevent abrasion and remove at flowering to allow pollination. Transplanted crops reach a later growth stage before beetles arrive than direct-seeded crops, giving them a leg up over this pest and the associated disease it vectors, bacterial wilt. Some repellents or systemics may be applied to transplants outside the greenhouse before setting in the field, which is convenient and allows lower rates of application.

Tomatoes: Powdery mildew was reported this week in high tunnel seedlings in Washington Co, RI. Low light and cool temperatures are the optimum conditions for this disease, therefore, early spring greenhouse and high tunnel plantings are particularly susceptible.


Wireworm: Was found feeding on roots of cabbage in a field in Franklin Co, MA and in a field to be planted in corn in NH. Wireworms often cause damage on potato and may now be feeding in freshly-planted potato seed pieces.  During extended hot, dry weather, such as we are having now, wireworms may seek out the potato tubers for moisture and food. Fields high in organic matter, recently plowed, previously in sod or pasture, or planted with grass cover crops, or low spots are more prone to high wireworm densities.  Avoid planting in these fields if possible. In NH, a farmer saw very high numbers of wireworm while plowing a field previously planted with daikon (Tillage Radish) and winter rye, without having to get off the tractor! The farmer is now reconsidering his plan to plant sweet corn in that field.

Garden Springtail: was spotted in a greenhouse in Burlington, VT on pak choi, in Bristol Co., MA on Napa cabbage, and was also reported on seedlings of multiple crops in MA. This tiny 1/16” blue gray (sometimes orange) insect produces shot holes in young leaves of many vegetable crops which resemble that of flea beetles.  They also spring off of plants as flea beetles might. Populations tend to be high in fields high in organic matter, with reduced-till systems, and with soils that crack when drying. Use clean cultivation and spot-treat areas where damage occurs. Most broad-spectrum insecticides registered for cutworms or leafhoppers will also control springtails.