April 14, 2003 Volume 12 No. 5 Update on Pest Management and Crop Development
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(Dave Rosenberger, Plant Pathology, Highland)
scab maturity counts
Spore maturity is advancing rapidly with the cool wet weather. The small number of empty asci in the Hudson Valley sample indicates that a few spores were released during cold wetting periods (35-37°F) that occurred April 5-8. Temperatures last Thursday, April 10, reached 54°F, but the leaf sample collected late on Thursday afternoon released only 22 spores in the tower discharge test, whereas we usually detect more than 120 spores in discharge tests a bit later in the season. Rain on April 11-12 generated our first Mills' infection period (25.5 hr wetting, 43°F) and may have allowed infections to occur in orchards that had high levels of inoculum and green tissue showing. Given the high level of spore maturity in the Hudson Valley, growers cannot safely postpone fungicide applications any longer. Warm weather predicted for April 14-17 will ensure that the next rainfall will trigger a significant spore release in most orchards.
The spore maturity noted for Geneva suggests that ascospores will be availalbe for discharge in that region by the time trees reach green tip.
(Art Agnello, Entomology, Geneva)
Temperatures that are downright balmy compared with what we saw only a few days ago are forecast for this week, and it doesn't take too long for the insects and mites peacefully snoozing in the environs to rise to the occasion with those things they do best -- fly, mate, and infest. Not all of this will take place at once, probably, but just to keep you mentally prepared for all the potential ambushes, here's a brief checklist of some prebloom arthropod concerns to consider before the season gets away from you.
Mites: Oil applications should go on before we reach pink or white bud in apples and pears, respectively, and as there's not much freezing weather in the extended forecast, any calm period of sufficient duration would be a suitable spray window. Start with 1.5-2.0% at first, and reduce to 1.0-1.5% as the trees reach tight/green cluster. In apples, Savey and Apollo can be delayed until pink, and if everything else runs away with your time and a miticide application before bloom is impossible, consider Agri-Mek at petal fall in problem blocks. Besides saving some time during the hectic pre-bloom period, this is also an ideal rotation material for purposes of resistance management.
Rosy Apple Aphid: In particularly susceptible varieties (Cortland, Ida Red, Golden Delicious, R.I. Greening), a material such as Lorsban or Supracide can provide effective prevention through tight cluster, and will pick up any San Jose scale at the same time. Actara is also a good prebloom fit for rosy apple aphid and other pests besides, including leafminers and early plum curculio.
San Jose Scale: Besides the Lorsban and Supracide noted above, delayed dormant oil applications will do a good job of reducing scale populations. If you're not treating for rosies but are concerned that SJS might be increasing in some blocks, Esteem is a new insect growth regulator with good activity on scale. The label calls for it to be mixed with oil, so if you're applying oil for mites anyway, this might be a tactic to try in severe cases.
Dogwood Borer/American Plum Borer: A coarse spray of Lorsban directed at trunk burr knots between half-inch green and petal fall is effective against both species that can be a problem in dwarf plantings.
Pear Midge: The first adults generally appear when Bartletts and Clapps are in the swollen bud to tight cluster bud stage, but no successful egg-laying occurs until the flower buds are a little more developed. In pear blocks with a history of midge infestation, concentrate on those portions of the orchard most protected from the wind by trees, high ground, or buildings, as the midges tend to be most numerous in these spots. Organophosphates like azinphos-methyl are the most effective materials; 2 sprays are recommended, one between late bud burst and first separation of the sepals, and another 7 days later (or at white bud, whichever comes first).
Pear Psylla: If you're just starting on your oil sprays, one application at 2% or two at 1% until white bud should provide adequate protection against egg deposition until an insecticide spray might be elected. Esteem at white bud or after petal fall has shown good activity in suppressing psylla numbers. Agri-Mek used shortly after petal fall has given good control if applied correctly (well-timed, adequate coverage, combined with an oil adjuvant), and split applications of Pryamite or Provado, also starting soon after petal fall, will keep nymph numbers down through the early summer.
Oriental Fruit Moth: The first adults could start flying during the next two weeks, depending on how long the warm stretch lasts, but we don't necessarily recommend pheromone disruption against this brood in peaches or apples, as your plum curculio sprays will serve double duty against OFM as well; however, be prepared to start these at petal fall in both crops, as shuck split will be too late to get the first egg-laying moths in peaches.
Severe damage to apples caused by phytophagous mirid bugs has increased in recent years. What we refer to here as mirids is a complex composed of mullein plant bug (MPB), Campylomma verbasci and apple brown bug (ABB), Atractotomus mali. Until recently, most reports of fruit damage in our area came from research orchards at the Geneva station, but increasing numbers of commercial orchards are starting to suffer damage; these bugs are already perennial pests in Canadian apple orchards, particularly in southern Ontario. Its very possible that some mirid bug damage has occurred regularly in N.Y. orchards over time, but has been mistaken for plum curculio scarring, which is capable of being quite variable in appearance. In western N.Y., MPB is more prevalent than ABB. These bugs are actually considered beneficial part of the season, being predators of pest mites and aphids. However, from bloom (when overwintered eggs hatch) until shortly after petal fall they may severely damage fruit.
Eggs of both species overwinter in the previous seasons spur wood, barely evident with only their tips protruding from the bark; hatch occurs at bloom time. MPB nymphs are small and lime-green in color, and can be confused with rosy apple aphid or white apple leafhopper nymphs, except that they move much more rapidly. They may have a reddish cast after feeding on European red mites. ABB nymphs are mahogany brown in color and slightly larger than MPB (refer to Insect Fact Sheet I25 for photos). Both species pass through five nymphal instars over the course of about 4 weeks. Adult MPB are small and green or brown with black spines and spots on their legs. They do not damage the fruit, but are predaceous. They may be found in fruit trees beginning about late June. Some may remain in the trees through the rest of the season. Most, however, migrate to mullein plants to lay eggs. In late summer or early fall, after another generation or two has been completed on mullein, the resultant adults will migrate back to fruit trees to lay overwintering eggs.
Damage to developing flowers or young fruitlets is caused by 1st generation nymphs of both species. Nymphs puncture the epidermis, which results in raised, corky, brown or black wart-like blemishes on the fruit. Some fruits will drop. On dark-skinned varieties like Red Delicious, minor blemishes may become less noticeable, and even disappear, as the fruit ripens. However, severe blemishes and malformation of the fruit, and minor blemishes on lighter-skinned varieties, will make the fruit unmarketable as fresh fruit. Some varieties appear to be more susceptible than others, although any variety can be attacked. Red Delicious, Golden Delicious, Northern Spy and Spartan are reported to be among the more sensitive, while McIntosh seldom suffers damage. We have seen severe damage in Empire, Rome and Crispin as well.
It is difficult to predict where and when mirid bugs may become a problem. Monitoring should begin in areas where damage was noted previously. Look also in areas that are in proximity to weedy areas inhabited by mullein or evening primrose. Mirid bug presence can be determined by tapping limbs with a length of hose or a stick over a tray covered with black cloth. Monitoring should take place every 2-3 days beginning at bloom and continuing through a week or so after petal fall. New growth, with a higher proportion of flower than leaf clusters, should be sampled by sharply tapping 2 or 3 times. It is suggested that 4 limbs on each of 10 trees (40 limbs total) be tapped in each separate orchard or block. More than 12 nymphs/40 limbs may be considered high. High populations can also be predicted from pheromone trap catches the preceding fall (more than 6/trap/day any time after Sept. 1).
Timing of insecticide application is critical but difficult to ascertain. The fact that the peak hatch period is during full bloom, when no insecticides may be applied, makes prevention of all damage unlikely. A chemical with relatively long residual activity, such as Asana or Actara, applied at pink, may provide control through the bloom period. Pink applications should be made as late in that growth stage as is safe for honey bees. At a certain (lower) density, petal fall applications of other materials may be just as good at preventing damage and are less harmful to predatory mites. These will kill most of the nymphs present, but some of the damage has already been done. Petal fall sprays in these cases should be applied as soon as possible after blossoms are off. Materials used for plum curculio or OBLR will control most mirid nymphs.
This material is based upon work supported by Smith Lever funds from the Cooperative State Research, Education, and Extension Service, U.S. Department of Agriculture. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture.
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