Allium Leafminer

The first flight of overwintering populations of Allium leafminers is expected to start next week. The second flight does not typically begin until September and extends into early October.

According to lab and field-based research at Penn State University, the best prediction for the emergence of adult ALM is based on the accumulation of 350 growing degree days (GDD), at GDD base temperature of 1°C starting January 1. For predicting site-specific adult emergence, weather data from NEWA (Network for Environment Weather Applications) can be extracted and calculated for the site. For April 20^th the forecasted GDD at 1°C base is 352 in Storrs and 373 in Bridgeport.

Allium crops, including leek, onion, shallot, chives, garlic, and green onion are susceptible to this pest. Some species of wild onion and ornamental alliums may be hosts as well, but the full host range is currently unknown.

Adults lay eggs in the top of an allium leaf making punctures. Scout for characteristic oviposition marks, as displayed in the image on the right.

The larva mine the leaves, creating tunnels of damage as they eat. These tunnels provide good entryways for fungal and bacterial pathogens to cause more damage to the plant. Larva will move down to the bulb, where they pupate either in the plant or drop into the soil.

The removal of infected host plants and other allium residues from earlier harvested alliums is an important practice for reducing potential outbreaks in fall allium crops. Insect exclusion netting or other types of row covers can effectively exclude ALM flies if securely applied before flight begins. Reflective mulch can reduce infestation levels, but is unlikely to provide enough protection to avoid economic damage. Foliar chemical applications have also been shown to be effective for reducing ALM damage. Two or three well-timed applications of an insecticide should provide an acceptable level of ALM control as long as the first application is 2- 3 weeks after initial detection of ALM flies and subsequent sprays are timed at 1–2-week intervals. Examples of highly effective insecticides applied as a foliar spray include dinotefuran (e.g., Scorpion), spinetoram (Radiant) and cyantraniliprole (Exirel). One OMRI- labeled option that works well is spinosad (Entrust). Other insecticides such as abamectin (Agri-Mek) and cyromazine (Trigard) can also help reduce ALM densities.

Cabbage Root Maggot

Cabbage root maggot is a pest of all types of brassicas, but is particularly damaging in cabbage, broccoli, Chinese cabbage, radish, turnips, and rutabaga. The first flight in April and May damages early spring brassicas, while a late summer flight from mid-August into September primarily injures fall root crops. Flies overwinter as pupae near roots of fall brassica crops and weeds.

Adult flies become active at about 288 growing degrees days (GDD, base temperature 40°F), which occurs 1-2 weeks after forsythia starts to bloom and when yellow rocket (winter cress, Barbarea vulgaris) blooms. GDD has just crossed this limit in Bridgeport, and forecasted to reach only 364 in Storrs on April 20. Fifty percent emergence (peak flight) occurs at about 450 GDD. 

Scout transplant trays before setting out plants in the field. A pencil is a good tool to gently stir the soil at the base of the plant and look for eggs. Yellow sticky cards placed near brassicas capture adult flies. In the field, finding an average of 1egg per plant can indicate a damaging population. Damage includes wilting, leaf discoloration, and plant death in leafy and heading crops and tunneling in root crops.

Row covers will protect the crops from cabbage maggots, flea beetles, and many other pests as long as the pests are not emerging from the same location. So, crop rotation is important. Soil drenches of Coragen, Verimark, Radiant, or Entrust can control the cabbage root maggot if applied when eggs are first seen at the base of plants. Research done in Cornell University found Verimark applied as a tray drench resulted in excellent control, but directed sprays at the base of the plant were the least effective. Verimark application as a soil drench also controls brassica flea beetles. Once larvae have been feeding in roots for several weeks, chemical control is difficult. See New England Vegetable Management Guide for pesticide options and restrictions in the application. For comparison of maggot fly biology for seed corn maggot, cabbage maggot and onion maggot, see Table 1.

Hardening off is the gradual process of getting transplants used to outdoor conditions before planting. It helps seedlings adjust to brighter light, wind, and cooler temperatures, and reduces transplant shock.

Start a week to 10 days before transplanting. Put plants outside in a protected, lightly shaded area at first, then increase their exposure to sun and outdoor conditions each day. A cold frame works well for this.

As plants harden off:

• reduce watering somewhat to slow growth, but do not let plants wilt
• protect seedlings from strong wind
• avoid setting plants out when temperatures are too low

Be careful not to harden plants too aggressively. The goal is to toughen them, not stop growth.

• Cool-season crops exposed to very low temperatures may bolt or, in broccoli and cauliflower, button.
• Warm-season crops should be hardened under milder conditions; cold can set them back and cause problems such as catfacing in tomato.
• Tender crops such as cucumbers and melons should not be left out overnight unless temperatures stay above 50°F
• Even hardy plants can be injured if exposed to freezing temperatures before they are fully acclimated

In general, ease transplants into outdoor conditions, keep them from drying out, and avoid damaging cold.

Upcoming Events & Opportunities

Save the Date!