RI Apple Newsletter
April 30, 1998
From Heather Faubert and Steve Alm
In this issue:
Updates on: Apple Scab, European red mite, Agri-Mek, apple blotch
leafminer, rosy apple aphid, European apple sawfly, white apple leafhopper
The recorded pest message is up and operating. Call between
5:00PM and 8:00AM for the latest message. New messages are recorded on
Wednesdays - for now. The number is (401) 949-0670.
We have had a total of 3 apple scab infection periods
so far this year: April 8, April 16, and April 23. We are expecting another
on May 1st. The wet period of April 26 was not an infection period - it
was wet for 20 hours at an average temperature of 40 degrees. At 40 degrees
it must be wet for 29 hours to cause an apple scab infection period.
We have not seen any apple scab lesions yet this year. It takes
9 - 17 days for scab lesions to appear after an infection period (depending
on temperature). We should be seeing them soon! Yesterday I quickly checked
some unsprayed McIntosh trees in an abandoned orchard but still did not
find any scab lesions.
We started finding hatched European red mites on April 20th. Check
the underside of oldest leaves to assess your early mite control. The
easiest place to find mites is generally on leaf clusters growing directly
out of largelimbs. 'Red Delicious' trees tend to have many of these clusters
growing right out of limbs so these are good trees to check. If you do
find many mites consider applying Agri-Mek at petal fall. Included here
is the new entry for Agri-Mek which will be in the new 1998 New England
Apple Pest Management Guide:
"Agri-Mek (abamectin): 0.15EC. 2.5 fl. ozs./100 gals. Higher
rate on label is for use on pear trees. Effective against leafminers (eggs
and sap-feeding larvae), European red mites, and two-spotted spider mites.
Apply in combination with horticultural summer spray oil or with a suitable
adjuvant. Oil rate should be minimum of 1 qrt. oil/ 100 gals. dilute.
Penetrants such as LI700 or Regulaid, or organosilicone surfactants such
as Silwet, Sylgard or Kinetic may be substituted, but efficacy may not
be quite as good as with oil. Effective application requires at least
40 gals. water per acre. Optimum timing for control of both leafminers
and mites is at petal fall. Applications made after two weeks past petal
fall will likely result in less leaf absorption and less residual efficacy.
Leaf surface toxicity typically lost within six hours of application.
Toxic action on pest species is due to translaminar movement of abamectin
into leaf tissue. Hence, Agri-Mek has long residual activity even under
high rainfall. Highly toxic to bees. Do not apply while bloom remains
on trees. Do not exceed 2 applications per season. See Mite Management
section for additional information. Restricted interval 12 hours. Preharvest
interval 28 days."
Agri-Mek information will also be included in table 18 - "Precautions
on Plant and Fruit Injury from Pesticides." The entry states, "Agri-Mek
in combination with horticultural spray oil may cause fruit injury to
certain varieties of apples, e.g. russeting on light skinned varieties
such as Golden Delicious, when used alone, or when other products are
applied sequentially. Carefully follow the Directions for Use and Precautions
on horticultural spray oil labels when combining with Agri-Mek."
Apple blotch leafminers were above the thresold of 21 moths per
red sticky trap by pink in 4 out of 11 monitored orchards. Three of these
orchards were well of above the threshold averaging 140 - 250 leafminers
per trap. The fourth orchard above threshold averaged 52 per trap. 52
is really not that far above threshold so we took a sample of flower clusters
and checked them under a 10x power scope to estimate how many eggs were
actually laid. At this orchard we found only 5 eggs out of 19 flower clusters
(about 125 total leaves on the 19 clusters). This number is quite low
and so an insecticide spray against leafminers should not be needed here.
At an orchard where we caught 250 leafminers per trap we found 49 eggs
on only 5 clusters! This grower is going to use Agri-Mek at petal fall.
Another choice for controlling apple blotch leafminers is applying Provado
at petal fall. Provado at 2 oz./100 gal. controls leafminers beautifully
and also controls white apple leafhoppers and rosy apple aphids.
Speaking of rosy apple aphids - we've seen more rosy apple aphids
this year than other years. The small aphids are causing leaves to curl
up now. They prefer fruit clusters, and feeding there causes small distorted
fruits and sooty mold growth. The only insecticide choice left for rosy
apple aphid control this season is Provado at petal fall. Cortland, Golden
Delicious, Idared, Gravenstein, Jonagold, and possibly Red Delicious are
more prone to rosy apple aphid damage. Check these varieties for tightly
curled leaves - and uncurl them to check for rosy apple aphids. Provado
at 2 oz/100 gal may be warranted if you find even just a few clusters
with rosy apple aphid. Provado is highly toxic to bees so be sure to wait
until all petals have dropped.
We started catching European sawflies on white sticky traps on
April 20th. No orchard has reached the threshold yet of 5 - 9 sawflies
per trap by petal fall. Being an early season, this year is a particularly
good one to monitor European apple sawflies. If sawfly trap captures
are low then a grower does not need to rush out at petal fall to apply
an insecticide. Rather, the grower with low sawfly trap captures can wait
until plum curculio are active before applying Imidan or Guthion. Plum
curculio prefer hot, humid conditions.
White apple leafhoppers begin hatching at pink and have completed
hatching by petal fall. The small, pale nymphs can be found on the underside
of older leaves.White apple leafhopper feeding removes sap from leaves,
causing stippling that may coalesce into silvery, white patches. Early
in the season, extensive damage may affect bud formation. White apple
leafhoppers are easiest to control when they are small, first generation
nymphs - from petal fall to early June (or perhaps mid May this year).
Sevin used as a thinner at 1 lb./100 gal controls leafhoppers. Provado
or Thiodan also controls them.
Newsletters, current pest reports, grower meeting information can be found
on our website at: http://www.uri.edu/research/ipm
Access to all New England newsletters and much, much more can be found
on the AIM (Apple Information Manager) website at: http://orchard.uvm.edu/aim