MOFGA's Pest Report - May 25, 2012
Compiled by Eric Sideman, PhD - MOFGA's Organic Crop Specialist
This last weekend of May is often the big weekend for growers. It is time to free the seedlings from the confines of the humid greenhouses and tight cell trays. But remember to be smart and not make things worse by putting pampered seedlings into conditions that may be too wet, or too cold, or too dry, or too sunny or make them vulnerable to attack. Those decisions have to be made on a local basis. Although many calls I am getting now are problems arising from seedlings being trapped in containers too long in greenhouses that get too hot and dry surprisingly fast, and in most cases it could only get better by getting the plants out into the real world of fresh air and soil, it could get worse.
COLD SOIL AND CUCUMBERS
A common problem seen by folks trying to rush the season is wilting cucumbers. Even without being killed by freezing, cucumbers can suffer a great deal and perhaps die from being in cold conditions. The small roots and root hairs of cucumber and other cucurbits give out in the cold. It may look like it is a sudden wilting of the plant due to drought, but really the problem comes on from the cold soil and then when there is a bit of sun or warmth and the plants need water they cannot get it, even if the soil has plenty to offer. Some parts of New England still have cold soil, although most places are plenty warm.
If you have delayed onion planting because things have not been right yet, or are replanting because the maggots got all the onions you put out earlier, then sunscald can be a problem. This is a problem that results from sudden hot weather. On hot sunny days the temperature at the soil surface gets very hot. The heat can damage sensitive young onion seedlings that are either just germinating or just set out as transplants. The injured tissue shrivels, strangling the neck right at the soil line, and the plant wilts and withers. The only way to avoid sunscald is to plant seed earlier in the spring so that the plants are beyond the sensitive stage before the soil temperature becomes too hot, or be lucky and not get hot sunny days when the tiny seedlings are sensitive.
The grubs that are the common problems in New England are the larvae of a bunch of beetles that may be a problem later in the year, such as the Japanese beetle, the Asiatic garden beetle, or the June beetle. The grubs live happily under sod and unless the populations are enormous, you may not even know they are there. Sod has lots of roots. But if you make a garden in an area that was lawn or some other sod, the grub population is the same size and the amount of root is much less. Quickly the grubs zero in on the crop and eat all the roots.
These species of beetles have similar life cycles but they do vary in number of years spent as a grub. The grub is causing the problems now for many new growers, or growers opening new fields. Later in the season I will get calls about the adults. Typically adults emerge from the soil in early summer to feed and mate. The females burrow into the soil (often in or near wide expanses of grass or sod) to lay eggs, usually beginning in late July and August. Eggs hatch into tiny grubs (cream-colored larvae, C-shaped, with brown heads). In late fall the grubs migrate downward through the soil profile, staying below the frost line throughout the winter. In the spring as the soils warm up, the grubs move back into the root zone and resume feeding. I am getting calls now about wilting plants that have few roots left.
There are not many controls for organic growers to choose from after the grub problem is discovered. Beneficial nematodes work fairly well on the grubs if there before the population explodes. The more technical term for these tiny round worms is entomopathogenic nematodes, and they have shown good efficacy when environmental conditions are favorable. Success with nematodes depends on proper application methods. Be sure to follow the instructions from the supplier carefully. A few suppliers of these insect-attacking nematodes are The Green Spot ( www.greenmethods.com), IPM Laboratories ( www.ipmlabs.com), and ARBICO ( www.arbico.com).
EUROPEAN CORN BORER CAPTURED IN MASSACHUSSETTS
(Reprinted from the UMass Vegetable Notes)
The first flight of European Corn Borer (ECB) has begun in warmer parts of the Connecticut Valley, in the plateaus near the river. Many thanks to the alert grower in Hatfield, MA who got his traps up and started catching moths! This is considerably earlier than the average emergence date for ECB. European Corn Borer overwinters as a late instar larva in the stalk of corn and other host plants. Its development into a pupa and then emergence as an adult moth is temperature-driven. The average degree day accumulations are almost double what they were at this time last year for many parts of the state, which is driving the early emergence.
Even if your corn is small, any farmers who are using traps to monitor flight should put them up as soon as possible to be able to tell if flight has begun in your area. Corn is still small, and most of the corn grown under clear plastic has yet to be cut out. If the predicted high temperatures of the coming weekend come to pass plastic corn will need to be cut free of high heat under the plastic. Once exposed, this larger corn is likely to attract egg-laying females ECB moths. Managing ECB in early corn, whether grown on bare ground or pushed ahead by plastic or row cover, can be tricky. Usually we wait until pre-tassel and scout for feeding damage and small caterpillars in the emerging tassel. When corn is in whorl stage as flight begins, eggs are laid earlier in the corn's development and there can be feeding at the whorl stage. ECB feeding in the whorl can be detected as pinhole leaf damage in the inner part of the whorl. When this happens large ECB larvae may still be around when ears form and their damage can slip by because it does not show up in the tassel.
There is no need for alarm; no one needs to rush out and start spraying corn. However it's worth paying attention and scouting closely for both flight and feeding damage on that valuable earliest corn. It has been found that when when ECB flight starts early and corn is infested in the whorl stage, a late-whorl spray can prevent ear damage in these early plantings.
We are still 1-2 weeks (depending on our GDD accumulation in the next week) from active feeding even in the warmer parts of the state where flight has started. In cooler parts of the state, flight will likely begin within the next 7-10 days. We know that more growers are using Trichogramma ostriniae, the tiny wasp that lays its eggs in ECB eggs. Timing is key for effectiveness: once eggs are hatched it’s too late! Any growers using Trichogramma ostriniae for control should be planning to release soon. The ideal time to release T. ostriniae is when eggs are in the field, but before eggs hatch. To be conservative, we prefer to release the same week that flight begins as the additional GDD for egg laying will very likely accumulate within that week. See charts below for degree days. Degree day information for many locations in MA can be obtained through the NEWA website ( http://newa.cornell.edu/). Note that the base temperature for ECB is 50 degrees Fahrenheit (10C). More information on using T. ostriniae can be found in our April 24 issue of Vegetable Notes, available at http://extension.umass.edu/vegetable/publications/vegetable-notes-newsletter/archives.
ECB first generation development
GDD (base 50F)
first eggs 450
egg hatch 550