Winter moth and scab update 4/27/14


All the winter moth eggs I was monitoring hatched by Thursday, April 24th. I was surprised to see 100% of the eggs hatched. Winter moth caterpillars can now be found inside blueberry buds, apple buds, and folded maple and cherry leaves. Supposedly they can be seen in some oak buds too, though the few oak buds I’ve looked at are still totally dormant.

This cool weather is delaying plant development, so winter caterpillars are quite protected inside buds and feeding. You can open buds and look for winter moth damage, frass, and/or caterpillars to see how well you have done controlling winter moth so far. The caterpillars are still tiny and difficult to see. The frass and damage is easier to see, but in most cases you still need to open up buds to see the damage.

If you find many winter moth caterpillars in apples or blueberries now, it may be helpful to spray an insecticide and hope the caterpillars move around enough to encounter the pesticide. It may be that you won’t be able to control them until the trees/bushes grow more so that the buds open up more and expose the caterpillars more.

According to NEWA – weather models online from Cornell – we did not have an apple scab infection period on Saturday, April 26th. We certainly had wet weather, but since it was so cold, it didn’t stay wet long enough to cause an infection period. I don’t know what was the average temperature was for yesterday, but at 45 degrees, 15 hours of leaf wetness (after it starts raining) is needed to cause an apple scab infection period. The NEWA apple scab model can be seen at:
You select the disease (apple scab) and then select the weather station (Providence, Newport or Middletown). The three RI sites are about 3/4 the way down the list of weather station sites – just below the CT sites and above the NJ sites.