RI Apple IPM Newsletter

From Heather Faubert and Steve Alm

McIntosh trees are at tight cluster in Rhode Island. So far cold temperatures have not been damaging to apple buds. Here is a chart of Critical Temperatures for tree fruit bud stages. This information was prepared at the University of Vermont by Jon Clements from material supplied by Joe Costante.

We did have an apple scab infection period from 4/8/98 – 4/10/98. The infection period took place over two wetting periods but we have to add the two wet periods together because the dry time between the two wet periods was not long enough. The two wetting periods added up to 36 hours of leaf wetness at an average temperature of 41 degrees. At 41 degrees, only 26 hours of leaf wetness is necessary to cause an apple scab infection period. The wet weather of 4/16/98 – ? will also be an apple scab infection period. It is much warmer this rainy period. At 50 degrees it takes only 11 hours of leaf wetness to cause an infection period.

Apple blotch leafminers have been caught on red sticky traps attached to trunks since April 6. The threshold of 8 leafminers per trap by tight cluster has been exceeded in 4 out of 7 orchards checked so far this week. In one orchard we have an average of 88 per trap. To control leafminers we recommend applying Provado or Agri-Mek at petal fall. Agri-Mek must be mixed with an adjuvant to be effective. It seems an oil spray, such as Sunspray Ultrafine Oil, is more effective with the Agri-Mek than a spreader sticker such as LI-700 or Silwet. Of course, combining Agri-Mek with oil causes complications when using Captan. Don’t use Captan within 10 days of an oil application.

Provado used at petal fall will also control white apple leafhopper and rosy apple aphid. Agri-Mek used at petal fall will also contol European red mite.

European red mites are still in the egg stage. As of 4/15/98 I did not find any hatched eggs. There is still time to apply dormant oil to suffocate red mite eggs. After tight cluster, oil should be applied at 1 gal/ 100 gal. Apollo or Savey can be used for mite control only if you did not use one of those miticides last year. Red mites can easily build up resistance to these materials so it is recommended to not use them any more frequently than once every other year. The same is true for Agri-Mek. If you used it last year, don’t use it this year.

Look now through pink for rosy apple aphids. Rosy apple aphids will attack all apple varieties, but varieties such as Cortland, Ida Red, Golden Delicious are particularly susceptible, and those in the McIntosh family are relatively tolerant. Rosy apple aphids are usually pinkish, sometimes varying to light brown, slate gray, or greenish black. The body is covered with a whitish coating. Don’t confuse them with harmless green apple aphids. Green apple aphid nymphs are clearly green, and without the whitish cast. Also, aphids found inside curled or distorted leaves at pink are almost always rosy apple aphids.

Sample 10 clusters from the interior of susceptible trees; sample 10 trees per block. If you find even one rosy apple aphid it is recommended to apply an insecticide at pink. Thiodan or Lorsban at pink will control rosy apple aphid. Synthetic pyrethroids (such as Pounce or Asana) are also effective but we do not recommend them since they are so harmful to predatory mites. Provado used at petal fall will also control rosy apple aphid but Thiodan or Lorsban at petal fall will not control rosy apple aphid sufficiently.

Our telephone hotline should be up and running on Monday, April 20th. Call between 5:00PM and 8:00AM for the weekly pest message. (401) 949-0670.