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Healthy Fruit 1998 Vol. 6:10

Jun 3, 1998

Weather From Oz

Tornadoes and thunderstorms that might as well be tornadoes &emdash; the extreme weather continues. The climatologists at the University tell us that with global warming, weather won't just be a bit warmer, it will also be more extreme. With the storms of last weekend, some orchards were hit by hail. As usual, the damage was spotty, but occasionally severe. Apple fruit across the state are approaching or just over 1" diameter. Peaches are also sizing. As the snow from the Dakotas approaches, we may have to rerun the "Damaging Temperatures" information. As Dave Chandler said, "Farmers are the ultimate gamblers because we are at the mercy of Mother Nature and every year is a new challenge." (Boston Globe, May 26) 

Apple Scab Popping Up

While the overall the apple scab situation appears to be under control, more and more scab spots seem to be appearing in orchards. The major effects of the early May rain should have appeared over 10 days ago, but rapid lesion development has been seen across the state over the last few days. Why? And more importantly, should anything be done about it?

There are at least a couple of theories as to why. For one thing, new lesions aren't always easy to see. Much of what has appeared in commercial orchards is spotty. It's on the ends of rows, in dense trees, or in the tops of large trees, all places which are difficult to spray. Unless you are climbing trees regularly and looking carefully, early lesions may not be seen until they have grown for several days beyond the time when a really close look might have revealed them.

For another thing, it has been relatively hot and dry since the monsoon rains. Beyond 80 degrees, scab development actually slows significantly. Instead of taking the 12 days that the average temperature would predict, high temperatures over 80 and dry days may have added several days to the time it took scab lesions to develop this year.

It may also be that some conidial scab overwintered in buds at the top of trees, though this is a longer shot. Usually primary infections from ascospores show up as distinct scab spots. Later, the conidia wash around on leaves, causing sheets and blotches of scab. There has been a lot of sheet scab this season, relative to most years. That may be from overwintering conidia. However, it is more likely that a very few primary infections from April spread rapidly during the rainy days in May.

If scab is there, it must certainly be kept in check. Spraying nothing, or even spraying with an EBDC during this last chance before the 77 day window closes, is not as effective as using full rates of captan, preferably with a benzimidazole (Benlate or Topsin M). Where scab is relatively light, this spray can be used as the first summer spray, and the effectiveness as a summer disease control can be estimated using Dave Rosenberger's chart (see below). That is, you should get 3 weeks of effective control. Then a straight captan schedule should suffice. However, keep an eye on things, and if the weather gets wet, or if it looks like the estimate of light scab was too low, follow up with another combination fungicide as close as one week after the first one.

If scab is more than "light", that is, there are at least 2 or 3 scab spots on every tree in an area, then that area will have to be treated with two eradicant sprays a week apart as described in last week's Healthy Fruit. And remember, it's still worth keeping scab down, even with a light crop. 


Rate per 100 gal dilute spray

Spray interval (days)

Maximum rainfall (in.)



Benlate +

3 oz


Mancozeb or

1 lb




1+1 lb


Topsin M +

3 oz


Ziram 76W or

1.5 lb



Captan 50W

2.0 lb


Ziram 76W

1 lb




Captan 80W

3/4 lb



San Jose Scaling Up

From 1993 to 1996, we received very few reports of troublesome populations of scale developing, and little evidence of SJS infestation was seen on fruit at harvest. Early-season oil programs are a good first step toward control of SJS, and these programs alone are generally very successful.

In 1997, a few blocks did develop high levels of scale damage. In areas where scale did become a problem, blocks of full standard-sized trees were the hardest hit, particularly in the top third of the canopy, where spray coverage may not have been optimal.

If the level of scale infestation has been increasing over the past several years, a pesticide treatment may be in order in the next couple of weeks. If such a treatment is necessary, a spray of Lorsban is the next step to avoid problems at harvest.

Curculio Still Hanging In

In our latest-developing monitored orchard (Conway), 259 degree days have been accumulated to date (as of 6/2). Over the past week, the average daily accumulation has been 13 DD (lower than was predicted in last week's Healthy Fruit). So, if accumulation continues at roughly 15 DD/day, this orchard will need about 5 more days of coverage, according the New York model. Because the weather has not been consistently warm, we have not blasted through the PC season. The tail-end of the season could produce surprisingly high and significant damage.

In four blocks where immigration is being tracked (by use of sticky interception panels), it is apparent that some PC are still moving into orchards. Damage in these blocks increased significantly last Saturday (excellent PC egglaying weather) as well, suggesting that late-arriving PC are still willing to oviposit, given the proper environmental conditions.

Due to these factors, we recommend that growers ensure that a solid protective cover is in place through this weekend, as rapidly expanding fruit and diminishing residual activity may open the door for late PC activity.

Mites and Leafminer Between Generations

Both leafminer and European red mites are between generations, and monitoring should be taking place to determine if treatments are warranted against the next wave of each. Leafminer development ranges from late sap-feeding mines to pupal development, but no second-generation adult flight has been observed thus far. Treatment against this generation of leafminer should be triggered by threshold levels of tissue-feeding mines.

To reiterate, we recommend that treatment be considered if more than 7 mines per 100 leaves appear on McIntosh, or 14 mines per 100 leaves on other varieties.

For ERM, our recommendations follow those developed in New York. At this point in the season, treatment should be considered if motile mites are present on 45% of fruit cluster leaves.

Stink Bug and Japanese Beetles Are Summer Peach Problems

A couple of years ago, we thought we'd take a step towards inventing peach IPM for New England. We did take a step &emdash; just not the one we expected. We sprayed test blocks at the HRC with either 4, 2 or no Imidan sprays, the thinking being that Imidan is a mite-friendly insecticide.

The treatments were as follows: ( All plots received standard calendar pesticide applications every 7 - 10 days until pit hardening in early June.)

  •  Treatment 1 - 4 applications of Imidan 70WP@0.75 lbs./100 gal. applied at approx. two-week intervals.
  • Treatment 2 - 2 insecticide applications (as in #1) at 2 and 14 July
  • Treatment 3 - NO insecticide sprays after pit hardening.

The bad news was that stink bug and Japanese beetle damage to peach fruits ('Redhaven' and 'Glohaven') did not differ significantly between four different insecticide protocols. Even applications of Imidan every two weeks did not adequately protect fruit. Since our plots were small, and we only used the one insecticide product, it is difficult to determine exactly why protection wasn't as good as we had expected.

But we confirmed our expectations that the major insect problems encountered on peaches at harvest were caused by stink bugs (or other Hemiptera) and Japanese beetles.

The bottom line for growers, at this point at least, is that it is likely there are critters, specifically stink bug and Japanese beetle, out in your peaches that can cause extensive damage late in the growing season. Be aware by monitoring. And keep protected with an insecticide if you have a history of problems. Insecticides recommended for stink bug include Thiodan 50 W(1.5 lb./100 gal.) Guthion 50W (8 oz./100 gal.), Lannate 90 SP (4 oz./100 gal.) and Penncap M (1 pt./100 gal.).

A Pair of Pear Pests

Pear psylla adult activity and egglaying are in full force, and the first summer generation nymphs were noted this week (6/2). Several blocks which received oil treatments alone are showing significant infestation, up to 15 or more adults per terminal and heavy egglaying. Most eggs have yet to hatch, and it is too early for treatment against the summer generation.

When sampling for pear psylla, it is also a good time to look for buildup of two-spotted mites on pear. At this growth stage last year, TSM were seen in moderate numbers moving into canopies, likely pushed into the canopies by mowing of the understory.

If mites become a problem on pears, they can be controlled by use of Vendex, Carzol, Kelthane or Pyramite. Pyramite is also labeled for use against pear psylla, but early data suggest that the cost of the high rate needed to gain control of psylla may be outweigh the efficacy.

New Pest Radar In Operation on the Web

Those of you with an Internet connection to the World Wide Web (by definition those of your reading this version of Healthy Fruit) may want to check out Glen Koehler's new method for using pest management models, the Orchard Radar. It will let you check on things like the potential for curculio damage, or the best way to treat for flyspeck given the weather. The gateway into the site is at

The Orchard Radar site consists of 35 tables and charts for each of 19 orchard sites in New England, including Belchertown, Sterling and Shelburne, MA.

User feedback is very much encouraged. Check it out.