RI Apple IPM Newsletter
April 17, 1998
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
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.
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