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