Unfortunately, closed greenhouses retain heat and humidity which can spell problems if left unchecked.

Remember, high relative humidity equals wet leaves which favor the development of fungal diseases such as Botrytis or bacterial diseases such as bacterial leaf spot. To avoid potential problems, do your best to vent out as much humidity as possible in the late afternoon and/or early morning. Turn on circular fans to promote air movement and finish watering earlier enough in the day so leaves have enough time to dry out before nightfall.

As a side note, stressed transplants where water and/or fertility have been withheld are also more prone to disease development. A light fertilizer application may go a long way in improving transplant health before setting in the field.

Please see Table E-14 and pages E52-E54 of the 2016-2017 Commercial Vegetable Recommendations Guide for a list of control options.

Note: The black light trap network has been deployed and is being monitored by IPM Program personnel. The corn earworm (CEW) pheromone trap network is not yet deployed. As adult European corn borer (ECB) and CEW begin to arrive in traps, population maps of these pests will be published in the Plant and Pest Advisory on a weekly basis. Additionally, maps of the brown marmorated stink bug (BMSB) will also appear in this publication. As the CEW pheromone traps in southern NJ begin to register catches, maps of these pest captures will also be published.

Cole Crops

Last week’s warm, sunny days, resulted in some infestations of crucifer flea beetle. Current cold, wet conditions are less favorable for flea beetle activity. These beetles can build to high populations quickly, especially where wild mustard and related cruciferous weeds are common. Mustard greens, radishes, arugula and Tuscan kale are favored hosts. Extreme feeding on small transplants can cause irreversible damage if not controlled promptly.

While flea beetles may be controlled with foliar applied insecticides, it is possible to get 2-3 weeks of protection by using a soil applied systemic insecticide at planting. This insures good establishment of the transplants without significant flea beetle injury.

 
As yet, no imported cabbage worm or diamondback moth larvae have been detected in new field plantings. As these pests appear, identification, scouting procedures and control measures will be outlined in the update.

Allium leafminer, a leafmining fly, was found about two weeks ago in Lancaster County, Pennsylvania. Since then the leafminer, which feeds on onions and related plants, has been found in four more counties in eastern Pennsylvania; Dauphin, Delaware, Chester, and Lehigh.  This is the first time that this fly has been found in the western hemisphere.  It belongs to the family Agromyzidae, which has many leafmining species.

The allium leafminer feeds on plants belonging to the onion group, including, leeks, onion, chives, shallot, green onion and garlic. The adult flies are cold tolerant and emerge in late February and March when the female, after mating, will lay eggs in the leaves of the host plant.  Upon hatching the larvae (maggots) will tunnel in the leaves eventually entering the bulb.  Reaching maturity the larvae will pupate as brown capsules between the leaves, in the bulb, or in the soil nearby.  They will go into a summer diapause with adult flies emerging in September and October to lay eggs.  The second generation larvae will mine leaves and pupate until time for adult emergence in the following February.
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• Dickeya sp., an aggressive form of Black leg, has been confirmed on potato in New Jersey in 2016. Symptoms of Dickeya infection look similar to Black leg infection and can cause significant rot above ground (stems and foliage) and below ground (tubers). All potato growers should scout on a regular basis and report any suspect plants or fields.
• There have been no new reports of cucurbit downy mildew.
• With the cool, prolonged wet weather, basil downy mildew may become active in greenhouses or high tunnels that have been closed up to retain heat. Appropriate venting to keep relative humidity low and leaf wetness to a minimum is critically important to keep the pathogen from sporulating and spreading rapidly.