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| Agriphones and Crop Updates Index Page |
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Vegetable Crop Update - Sweet Corn, Beans and Pea Edition European Corn Borer - Accumulated Growing Degree Days European Corn Borer - Accumulated Growing Degree Days Univoltine corn borer adult populations peak at 650-700 GDD. The second generation of bivoltine European Corn Borer adults usually emerge at 700 GDD. The population peaks at 1050-1100 GDD.
We have had a fairly active year for aphid populations and as a result we are starting to see viral diseases show up in the vegetable crops. Soybean aphids will only establish colonies on soybean plants. However, they can land and temporarily feed in other crops before moving on to the next soybean field. This transient feeding results in the rapid spread of viruses between different crops. Viruses such as the bean common mosaic and the cucumber mosaic are spread almost instantaneously, as the aphid begins to feed. As a result, chemical controls targeting aphids rarely ever reduce the level of viruses in any given field. The offending aphids are long gone by the time the sprayer hits the field. In beans, the virus diseases will cause mottled green-yellow discolouration on the leaves. Leaves often become twisted or puckered. Infected pods are usually distorted or “curly” shaped. This is may be accompanied by brownish-purple streaks on the pods. Occasionally, infected pods will develop on plants with no noticeable leaf symptoms.
Figures 1 & 2 Virus Symptoms on Leaves and Pod
It is important to protect bees when spraying insecticides. Honeybees, as well as other bees and insects, are important crop pollinators. Bees often visit sweet corn fields to collect water and pollen. This is especially common during dry weather conditions, when wild sources of pollen become less available. Most organophosphate and carbamate insecticides are highly toxic to bees. Wherever possible, avoid spraying sweet corn while the tassels are producing pollen. Optimal control of the European corn borer occurs when an insecticide is applied as the tassel emerges from the whorl. Late spray timing is a common cause of control failures. Monitor corn fields regularly for egg masses and pin-hole feeding. The economic control threshold is 5 percent of the plants with eggs or pin-hole feeding damage. Larvae must be controlled before they begin to bore into the leaf veins and stalks. Insecticide applications after boring has occurred will do little to control the population. Be aware of any bee hives within a 2-3 km radius of any sweet corn fields, especially if neighbouring crops require bee pollination. Cucumber, melon and squash growers commonly use honey bee colonies as pollinators. A list of local beekeepers can be obtained by contacting the Provincial Apiarist at 1-888-466-2372. Spraying after 7 pm when the bees are not foraging is a good management practice. This will give the spray residue ample time to dry before the bees enter the field the next day. If possible, choose a product or a formulation that is less hazardous to bees. Prevent drift. Do not apply pesticides on windy days. Communication between sweet corn growers and beekeepers is vital to help prevent bee poisonings associated with sweet corn. Bee Keepers should take the following steps to protect their bees:
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