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Healthy Fruit 1997 Vol. 5:4

Apr 30, 1997

Growth Stage. . . Development Still Slow

Across most of the state, orchards are at 1/2" green to tight cluster, with the latest-developing areas are green tip. The development has been somewhat slower than in previous years; most orchards were at early pink at this time last year.

First Scab Infection Period in Many Areas

The rain on Sunday night and Monday made for an interesting scab infection period call. Temperatures across the state during the wetting ranged from the high 30's F to the mid 40's F. Therefore, the hours of wetting required for infection ranged from 28 hrs. to 13 hrs. Taking the nighttime wetting into account (the rain began at night), most wetting periods were in the range of 18 to 24 hrs. from day break on April 28.

That means, in most of the state, the wetting was an infection period. It is possible that in some colder areas, wetting was not long enough for infection, and growers in these areas still don't need to worry about scab fungicide applications. Everyone else does!

Assuming the last rain was an infection period, then either the trees were protected or they weren't. If you sprayed a fungicide within the week before April 28, all should be well, and you don't need to worry until the next rain. If you were not protected, then a treatment is in order. As I write this, we are already 50 hrs. from the start of the infection, and by the time you get this in the mail, we will be well beyond the 96 hr. official post-infection window for Nova or Rubigan. However, all isn't lost if you did not apply anything yet.

Two applications of Rubigan or Nova 7 days apart applied prior to symtoms showing will generally stop scab. Once symtoms show, then there are real problems. More on that in a later newsletter.

Rust Spots

Fortunately, we in Massachusetts do not have heavy disease pressure from either cedar apple rust or quince rust, the most important apple rusts in the Northeast. However, these diseases can be a problem in some areas, along the North Shore, for example, where the alternate host for cedar apple rust (the eastern red cedar) is abundant. For these growers, it is important to use a fungicide which will control rusts as well as scab in those sprays applied from tight cluster through bloom. This is when fruit is most susceptible, and rust inoculum is most abundant from pink through petal fall.

Big Leafminer Catches Indicate a Need to Treat

In the earliest-developing areas of the state, some orchards have already reached very high populations of leafminers on sticky red rectangle trunk traps. For example, in half of the orchards sampled, LM have reached 50 per trap, which is well over the trap capture threshold for treatment.

In mid- and late-developing orchards, trap captures are still fairly low.

The weather during some recent evenings has been favorable for LM egglaying; relatively calm conditions with temperatures greater than 55o F about an hour or two before dusk. In fact, a sizable number of freshly laid eggs was observed (more than 1 per leaf cluster) on the oldest leaves in one orchard in Wilbraham at late tight cluster.

We do not know at this time whether high leafminer trap captures in earlier-developing orchards will be characteristic of the state for two reasons. First, the very high populations may be limited to orchards which did not use an application of pesticide against LM last season, thus their last LM treatment was in the 1995 growing season. Second, in the earlier orchards, a larger proportion of the larvae from the last generation of 1996 may have been able to complete their development before the cold weather set in. This may not have been the case in the later-developing orchards.

That notwithstanding, in our judgment this could be a big year for LM in Massachusetts, especially given the likelihood of a high rate of overwintering survival. Orchards which did not receive a treatment against LM last year may be particularly vulnerable to the development of high populations early in the season. In last week's issue of Healthy Fruit, we gave the trunk trap capture thresholds which in our experience merit treatment either at pink or petal fall. Also in last week's issue, we discussed insecticides which can be used to treat for leafminer.

To recap, we highly recommend either a treatment of Provado at petal fall or Agrimek (in conjunction with 1% refined horticultural spray oil) at petal fall or first cover. Merck (the manufacturer of Agrimek) recommends refined horticultural spray oil rather than unrefined dormant oil for use with Agrimek in order to pose less of a threat of incompatibility with a fungicide program which involves the use of Captan.

It is absolutely essential that an emulsifier (such as hort. spray oil) is used with Agrimek to permit the material to penetrate the leaf tissue for efficacy against LM larvae. We recommend treatment with either Provado or Agrimek against LM, but each has certain advantages, depending on the specific orchard situation. Provado has the advantage that it will provide season-long control of both leafhoppers and aphids, but it is ineffective against mites. Agrimek holds the advantage that it offers very effective control of mites through July, but it is not effective against either leafhoppers or aphids.

Scarcity of Plant Bugs

So far, tarnished plant bug populations are relatively low across the state. Very few blocks average greater than 1 TPB per trap, which is well below threshold for treatment. Additionally, there are few indications of feeding or direct observation of TPB active on fruit clusters. Like last season, 1997 bears the potential for light activity but given a few warm days in a row there may be an increase in activity.

Some bud abortion has been observed, which appears to be more related to cold weather injury than to plant bug activity.

Leafrollers Snacking

In a couple of orchards, a few leafroller larvae have been seen chomping on flower buds. Usually, LRs are controlled very well by the pre-bloom insecticide applications and damage remains low enough that even if no pre-bloom insecticide is applied, the petal fall plum curculio spray offers good control.

Still Waiting on Mites

Although there has been no observed egg hatch yet, this should begin to occur in the next couple of days in the earliest orchards. Thus far, it has been a fairly good spring for oil applications. If a double-oil program is being used, the treatments must be applied by late tight cluster to early pink (before egg hatch) at the latest in order to be most effective as an egg suffocant. See last week's issue of Healthy Fruit for a detailed discussion of options for mite control.

Psylla Start

Pear psylla eggs have begun to hatch in the earliest areas, but the hatch is not far along as yet. We would advise that the last application of 1% oil against psylla occur between green cluster and early white bud but no later in order to avoid potential damage to the buds.

Apple Info in Cyberspace

The electronic age continues to arrive, if somewhat slowly, to the New England apple industry. There are a couple of options for those growers wishing to get Healthy Fruit faster than the regular mail will deliver it. A text version can be gotten by email to your address, if you let me know what that address is. Contact me at and I will get you on the email list. Alternatively, you can look up Healthy Fruit on our Web site at the UMass Extension Fruit Program.

From here, you can find valuable weather information, IPM information, and participate in grower exchanges. We encourage you to try these out.

Aliette and Fire Blight

Fire blight infection periods are a few weeks away. However, an interesting question came up about the potential for Aliette (fosetyl Al) to manage the disease. The label says that "Aliette used in a program with other registered bactericides and recommended sanitation measures aids in the control of Fire Blight caused by Erwinia caratovora." They recommend starting applications for this purpose as early as tight cluster.

Checking on this, I found very little support for the use of Aliette among apple pathologists who have worked with fire blight. While there have been a few positive tests, most evaluations were negative. The comment on the label appears to be a bit like the ads for kid's cereal, where some confection made of sugar and food coloring is promoted as "part of this complete breakfast", where the picture of the breakfast includes orange juice, toast, milk and half a grapefruit. Out of half a dozen researchers who replied to my question, not one felt that they would recommend Aliette as a control for fire blight.

Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, and Wes Autio, except where other contributors are noted. Final copy is edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Please cite source if reprinting information.

Daniel Cooley