Eric Sideman's Pest Report
July 28, 2003

(View List Of All 2003 Pest Reports)

SWEET CORN

European Corn Borer: Pheromone trap catches have continued to be significant in locations last week. Borer moths are laying eggs on any corn plants available, including those in silk. Silking fields should be protected when 5 or more moths are caught in a week. Sprays for European corn borer were recommended on silking corn in Litchfield, Oxford, and Waldoboro. European corn borer feeding damage exceeded the threshold for tassel corn in Biddeford, Cape Elizabeth, Dayton, Lewiston, Litchfield, North Berwick, Oxford, Poland, and Wells. Fields with European corn borer damage should only be sprayed if fresh feeding injury is found on 30% or more of the plants scouted in a field. Once the corn reaches the pre-tassel stage, the control threshold is lowered to 15%.

Corn Earworm: Corn earworm moth catches in pheromone traps rose significantly in southern and central Maine. Get out the Zea-Later in areas where moth counts are up. Typically, fields that are not silking do not need to be protected from corn earworm, unless larvae are found feeding on foliage and damage exceeds the 15 or 30% threshold when added with other feeding injury.

Fall Armyworm: Fall armyworm moth trap catches have risen this week. This is an early arrival of this insect, which is typically the last serious corn insect pest to arrive in Maine. The threshold for silking corn is 3 moths per week. Moths were over threshold in Biddeford, Cape Elizabeth, Dayton, Lewiston, Monmouth, New Gloucester, and Oxford. There has not been any significant feeding injury found. Armyworm moths prefer to lay their eggs on young corn plants. When found, this injury is combined with any European corn borer injury to determine if protection is needed. Control thresholds are 30% infestation in whorl stage corn or 15% for corn at pre-tassel and beyond.

If you have any questions about insect trapping or field scouting corn, we'd be happy to help. Call Highmoor Farm at 933-2100 or the Pest Management Office at 1-800-287-0279.

(modified from Sweet Corn Report, David T. Handley Vegetable & Small Fruit Specialist)

USING THE ZEA-LATER TO CONTROL CORN EARWORM

Timing: Corn should be treated with 0.5ml of corn oil and Bt once during silk when more than 2 corn earworm are found per week in a trap in your area. The ideal age to treat the corn depends on the temperature. The best time to apply oil is generally 5-6 days after silk growth starts, or 3-4 days after the silk is fully-grown. At this time, the tips of the silks have begun to wilt and turn brown and pollination is nearly complete.

Within a field, plants grow at different rates and begin silking at different times. In a relatively even stand, silk emergence is concentrated in a 3-4 day period. To determine the best time for oil applications, note the day when 50% of the corn has begun to show silk, and count from that date.

Applications made earlier than 5 days after silk do not appear to give better control, but may result in a higher rate of "cone" tips. This occurs when oil interferes with silk pollination resulting in unfilled kernels in the last half-inch of the tip. While partially filled tips are a relatively common occurrence in sweet corn, cone tips caused by oil are more pronounced.

Oil applied later than 8 days after silk initiation can result in more feeding damage to the kernels caused by caterpillars that entered the ear prior to the oil. There is a window between 5 and 8 days after silk initiation that provides the best combination of corn earworm control and ear fill.

The timing can also be determined by husking a representative ear and examining the kernels. The ideal time to treat it is when the silk is still attached to the top 1" or less of the kernels.

Materials: We recommend using corn oil with an added Bt. Organically certified growers will need to use a dry formulation of Bt and add an emulsifier to the oil to keep the Bt suspended in the oil. We have had luck with liquid lecithin. Add 5% volume of liquid lecithin to the oil before adding the Bt mixed in water. Liquid lecithin is the consistency of molasses: we strongly recommend that you add it directly to the oil instead of measuring into a separate container first. Lecithin will mix more readily with oil than water, making cleanup difficult: be careful not to spill the lecithin.

Use the labeled rate of Bt per acre in corn. Add this to the approximately 2 gallons of oil it takes to treat 1 acre. For the Dipel DF product that we used in our trials this translated to approximately 3 tablespoons of Bt per liter of oil for an application rate of 1/2 lb Bt per acre.

If you have any questions please contact Pam Westgate at westgate@umext.umass.edu or 413-545-3696.

(from report in UMASS Veg Newsletter,P. Westgate)

JAPANESE BEETLES

Controlling adults is very hard. On a small scale I suggest going out every morning with a jar of soapy water and just tapping the beetles in. On a larger scale I do not have much advice. I am trying Surround this year and it seems to reduce the numbers. But it does not get the numbers to zero. Remember, it coats the plant with the white clay so it does not make sense when fruit is present because it will be hard to market.

SQUASH AND PUMPKINS:

Resistant cultivars are available and should be used if you have a history of powdery mildew. Crop rotation can work if your fields are far apart.

Spray materials include copper (Champion), baking soda (homemade) or potassium carbonate formulation (Kaligreen). Spray programs should begin at first signs.

POTATOES

(About the author: Eric is MOFGA’s Technical Services Director, essentially an organic "extension agent". He can be reached at the MOFGA office to answer your questions about farming and gardening. Link to MOFGA Contact Page, or email Eric directly.)