June 28, 2004 Volume 13 No. 15 Update on Pest Management and Crop Development
* = 1st catch
Geneva: Obliquebanded leafroller flight began 6/7.
Sampling should take place at approx. 600 degree days (base 43F) following
this event. DD accumulated since then = 400.
Oriental Fruit Moth
Spotted Tentiform Leafminer
Oriental Fruit Moth
Spotted Tentiform Leafminer
Oriental Fruit Moth. This pest's development is tracked using a 45°F DD model from biofix, defined as the first sustained moth catch. We are currently between the first and second brood, for which the first catch is not expected to occur for another 5-7 days in WNY; 2nd brood flight should have begun already in ENY.
Codling Moth. We are currently between the first and second brood control windows for this pest. With 1260 DD (base 50°F) from the 1st catch of the season as a first spray date for the second brood, we currently have:
Obliquebanded Leafroller. First hatch is predicted at approximately 360 DD (base 43°F) from the 1st catch, and 25% egg hatch at 450 DD. Our sample numbers so far:
The overwintered eggs hatch from mid-April through May and the nymphs (crawlers) migrate from the oviposition sites to their feeding sites on terminal growth and leaf undersides of trees and shrubs. This hatch is completed by the petal fall stage of pears. Nymphs that hatch from these overwintered eggs are active from roughly early May to early July. As the nymphs approach the adult stage, they tend to congregate on older branches at a pruning scar, a node, or at a branch base, as well as inside the calyx of pears. Second- (summer) generation nymphs are present from about mid-July to mid-September.
The Comstock mealybug poses two major concerns for the pear processing industry of New York: First, the emergence of crawlers and adult females from the calyx of pears at the packinghouse creates a nuisance to workers. Second, pears to be made into puree typically are not peeled or cored by New York processors, so infestations can potentially result in unacceptable contamination of the product.
Another problem, of concern to apple growers in the 1930s and 1940s, and again in the Hudson and Champlain Valleys in the early 1980s, is that the honeydew secreted by the crawlers is a substrate for sooty molds growing on the fruit surface. This type of damage has also been noted on peaches in Niagara Co. and in Ontario, Canada. These molds result in a downgrading of the fruit, and are therefore an additional cause of economic loss.
To date, the Comstock mealybug has been a problem to growers of processing pears because of the contamination and aesthetic reasons noted. An infestation generally requires one or more insecticide sprays during the growing season, directed against the migrating crawlers. Examine the terminal growth for crawler activity periodically throughout the summer. Crawler and adult female activity can also be monitored by wrapping double-sided tape such as white carpet tape around low scaffold branches and inspecting for crawlers that have been caught by the tape. They can be recognized with a hand lens or, with some experience, by the unaided eye.
Sometime in early August, we'll advise an application of a material such as Provado, Diazinon, Actara, Assail or Lannate to control this insect.
Dilute trunk applications of an insecticide with good residual activity can provide control of established infestations. Lorsban 4E or 50W may now be used postbloom as a directed trunk spray in N.Y. for borer control in apples. We feel that Lorsban is the best tool we presently have for this use, and mid-July would be a good time to take advantage of this welcome opportunity to use it on apples to control both dogwood borer and the second generation of American plum borer. Another option at this point in the season is an application of Thiodan 50WP applied once during this first week of July, and again one month later at the beginning of August. We would also note that, in case you didn't follow the strategy of using Lorsban as a prebloom trunk spray for American plum borer, these treatments will also serve as the last opportunity for a control measure against this pest.
apple aphid (WAA), Eriosoma lanigerum (Hausmann)
Aerial colonies occur most frequently on succulent tissue such as the current season's growth, water sprouts, unhealed pruning wounds, or cankers. Heavy infestations cause honeydew and sooty mold on the fruit and galls on the plant parts. Severe root infestations can stunt or kill young trees but usually do not damage mature trees. Large numbers of colonies on trees may leave sooty mold on the fruit, which annoys pickers because red sticky residues from crushed WAA colonies may accumulate on their hands and clothing.
Water sprouts, pruning wounds, and scars on the inside of the tree canopy should be examined for WAA nymphs. Any new growth around the outside of the canopy should be examined for WAA colonies. No economic threshold has been determined for treatment of WAA.
Aphelinus mali, a tiny wasp, frequently parasitizes WAA but is very susceptible to insecticides and thus does not provide adequate control in regularly sprayed commercial orchards. Different rootstocks vary in their susceptibility to WAA. The following resistant rootstocks are the only means of controlling underground infestations of WAA on apple roots: MM.106, MM.111, and Robusta.
WAA is difficult to control with insecticides because of its waxy outer covering and tendency to form dense colonies that are impenetrable to sprays. WAA is resistant to the commonly used organophosphates, but other insecticides are effective against WAA, including Diazinon and Thiodan.
Sooty blotch and flyspeck (SBFS) are two of the most important summer diseases of apple in New York. The diseases do not result in direct losses in yield, but rather they cause a reduction in fruit quality, which can lead to economic loss due to downgrading in fresh market fruit. Losses can exceed 25%, especially in warm humid climates such as those experienced in southeastern NY, southern New England, and the mid-Atlantic and southern states. Until recently, sooty blotch was thought to be caused by the fungus Gloeodes pomigena. However, recent studies have shown that sooty blotch is a disease complex caused by at least 3 different fungi: Peltaster fruticola, Leptodontium elatius, and Geastrumia polystigmatis. All three fungi are not necessarily present in all sooty blotch lesions. Flyspeck is caused by the fungus Schizothyrium pomi (= Zygophiala jamaicensis).
Flyspeck appears as distinct groupings of shiny, black fungal bodies (called thyriothecia) on the surface of the fruit. The number of thyriothecia associated with a single infection ranges from a few to over fifty. Although flyspeck thyriothecia appear to exist individually, close examination reveals mycelium connecting the individual structures. The primary spores are discharged starting around 2 weeks after petal fall and symptoms may be visible 10-12 days after infection under optimal conditions, but may not be visible for 1 month under less than ideal conditions. These primary infections will give rise to conidia, which initiate secondary cycles of infection throughout the remainder of the season. Numerous observations in the field have shown that warm and wet or humid conditions are needed for the development of disease. For both flyspeck and sooty blotch, the causal fungi grow only within the wax cuticle of the fruit and are quite superficial. Rubbing the fruit with a cloth will often be enough to "clean-up" an apple that is only lightly affected.
The primary means of managing sooty blotch and flyspeck is via fungicide applications during July and August. Four or five summer fungicide applications may be needed to control these diseases in wet years, whereas only two or three well-timed applications are needed in dry years. Fungicides applied to control scab and mildew at petal fall and first cover are usually adequate for protecting apples from flyspeck ascospores. In the northeast, the fungi causing sooty blotch are generally more sensitive to fungicides than is the flyspeck fungus, so flyspeck almost always appears first in orchards with marginal fungicide protection. Summer fungicides timed to control flyspeck will almost always provide adequate control of sooty blotch.
Following discharge of flyspeck ascospores during the 2-3 weeks after petal fall, the risk of flyspeck infection is relatively low until the time when ascospore-initiated infections in hedgerows and woodlots begin producing conidia for secondary spread of the flyspeck fungus. This seems to occur after about 250-280 hr of accumulated wetting after petal fall (AW-PF) on apples. During this interval from 3 weeks after PF until 250 hr AW-PF, the risk of SBFS infection on apples is relatively low and fungicide coverage can usually be relaxed (provided, of course, that primary scab has been completely controlled). Beginning at 250 hr AW-PF, however, the risk of secondary flyspeck infections gradually increases until harvest.
Research has shown that Topsin M, Sovran, and Flint provide post-infection activity against sooty blotch and flyspeck. Their post-infection activity decreases as the time between infection and fungicide application increases. Although there are still some data gaps with Sovran and Flint, tests completed to date suggest that all three of these fungicides have reasonable activity against flyspeck infections if the fungicides are applied before infections are exposed to 100 hr of accumulated wetting. Working in North Carolina, Brown and Sutton (1995) showed that sooty blotch and flyspeck appear on fruit only after fruit are exposed to 275-300 hours of accumulated wetting following infection. Thus, it appears that Topsin M, Sovran, or Flint will provide post-infection control of flyspeck and sooty blotch so long as the infections are less than one-third of the way through the incubation period.
When Topsin M, Sovran, or Flint are used for July-August sprays, the period of relaxed fungicide coverage in June and early July can probably be extended until 350 hr AW-PF (250 hr for development of flyspeck conidia plus 100 hr of post-infection activity). Even in dry years, however, trees should probably be protected with fungicides during the latter half of July because fungicide spray coverage later in the season may be compromised as apple size increases (thereby increasing contact surface areas between adjoining fruit) and as limbs bend down under crop load. Should a dry summer suddenly turn wet in August, SBFS could cause huge losses in orchards that were not protected prior to the rains.
Pre-determining the timing for the last SBFS spray in August or September is impossible because the need for additional sprays during that period is based on the weather. Last year at the Hudson Valley Lab, we recorded nearly 3.5 inches of rain in the first two days of September and then accumulated 270 hr of wetting by 30 Sept. Growers who did not re-apply a fungicide after the rains of 1-2 September noted that flyspeck seemed to appear overnight at the end of September on fruit that were not yet harvested. The trick to correctly timing the last fungicide spray in 2003 was to correctly guess how many hours of wetting would accumulate after the rains of 1-2 September and before fruit would be harvested. (Remember that 270 hr of wetting are required to complete the incubation period.) Growers who gambled on a dry or even a "normal" September lost that bet in 2003. Those who applied fungicide during the first week of September (on the assumption that September would be wet) were the winners in 2003.
Although an early September spray may be needed in exceptionally wet years, sprays applied during late August and September will not compensate for coverage gaps during July and August because none of our fungicides can completely eradicate SBFS after infections on fruit are older then 100 hr of accumulated wetting. Therefore, sprays between early July and mid-August remain the most critical timing for controlling SBFS under NY conditions in most years. Earlier and later sprays are needed in wet years, but two or 3 applications between 15 July and 15 Aug are almost always essential.
Brown, E.M., and Sutton, T.B. 1995. An empirical model for predicting the first symptoms of sooty blotch and flyspeck of apples. Plant Disease 79, 1165-1168.
Cooley, D.R., Gamble, J.W., and Autio, W.R. 1997. Summer pruning as a method for reducing flyspeck disease on apple fruit. Plant Disease 81, 1123-1126.
Williamson, S.M., and Sutton, T.B. 2000. Sooty blotch and flyspeck of apple: Etiology, Biology, and Control. Plant Disease 84, 714-724.