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Volume 6, No. 7
May 20, 1998

Weather Woes Continue

The days of rain during bloom may have had more of a lasting effect on pollination and set than on disease or insect activity. The state is past bloom, and fruit size, where there are fruit to size, is as follows:

• Ashfield 1/8 in.
• Belchertown 1/4 in.
• Northboro 1/2 in.
• Sterling 1/2 in.
• Wilbraham 1/2 in.

• Assess set carefully to determine management needs.
• Check for scab.
• Continue curculio monitoring.

It is clear from grower conversations and scouting reports that McIntosh are few and far between this year. Why? It likely is related to a combination of factors, but poor bloom weather and bee flight probably are the major causes. Regardless of the cause, however, many growers are faced with the decision of whether or not to manage a nearly missing crop.

First, it is extremely important that you allow adequate time to pass before assessing final fruit set (or estimated final set). Do not abandon the crop before you really know. Secondly, make sure to evaluate set in a rigorous and systematic way. We all can remember years where we have expected very few apples and they miraculously appear in July.

The last consideration is economic. Specifically, will you make more money (or lose less money) if you abandon the crop or manage it normally? We have developed a few scenarios below that may help you make this decision. These data are based on averages of wholesale costs and returns and estimates of fruit size relative to crop level.

The starting point (a full crop) is an estimated 600 bushels per acre, mostly 120's with some 140's. This is not the crop recommended that you grow for today's market, but unfortunately it's the one that's still often grown. As fruit number declines, yield declines, and fruit size increases. For today's market, this is good, in terms of profit. The distributions among 80/96's, 120's, and bags varies with average size. In all cases, 15% of the crop goes to juice.

The table on the next page shows the results of the interacting size and investment factors. As usual in today's market, producing a full crop of 120's and 140's for the wholesale market results in a loss of over $1,000 per acre. Two thirds of a crop loses only $135 per acre. Fifty percent of a crop is the most profitable, resulting in net returns of over $300 per acre. A 25-percent crop results in a $5 loss per acre, and a 15-percent crop loses $660 per acre. So, the only thing worse than losing 85% of a crop is growing a full crop of small apples!

If the crop is abandoned, three to four pesticide sprays will be saved and no money will be expended on picking, packing, storing, or marketing. However, about $1,000 per acre of costs have been or will yet need to be expended this year. Therefore, abandoning the crop, regardless of the cropping level, will result in about a $1,000 per acre loss.

If managing the crop results in more loss than abandoning it, then abandonment is a good decision. With these scenarios, the only situation where managing the crop costs more than abandonment is with the full crop. Even as few as 100 bushels per acre will result in less loss than abandonment. Carrying the data beyond the table shows that 50 bushels is about the cutoff point. That is, producing less than 50 bushels per acre (about 8% of a full crop) will cost more than abandonment. Clearly, these are only estimates, and everyone considering this decision should make the same calculations that we have using their own numbers.

Category	Full crop	67% of full	50% of full	25% of full	15% of full
Fruit quantity (number/acre)	76,000	51,000	38,000	19,000	7,600
Yield (bu/acre)	600	470	380	230	100
Average size (g)	150	175	190	230	260
Costs and returns if pests are managed and crop is harvested and sold
Fruit return ($/acre)	5,258	5,060	4,744	3,190	1,390
Growing costs ($/acre)	1,200	1,200	1,200	1,200	1,200
Fruit costs ($/acre)	5,100	3,995	3,230	1,995	850
Net return ($/acre)	-1,042	-135	314	-5	-660
Costs and returns if spraying was discontinued and fruit were abandoned
Fruit return ($/acre)	0	0	0	0	0
Growing costs ($/acre)	1,000	1,000	1,000	1,000	1,000
Fruit costs ($/acre)	0	0	0	0	0
Net return ($/acre)	-1,000	-1,000	-1,000	-1,000	-1,000

Averages per bushel used to estimate fruit return were: 80/96's = $16.00; 120's = $11.00; bags = $9.00; and juice = $2.00. Overall picking, storing, packing, trucking, and marketing cost used was $8.50 per bushel.

Growers should know by the end of this weekend whether scab infections occurred in the middle of all the wet weather. Primary scab inoculum is gone. Now is the time to look carefully for any developing lesions.

What if scab lesions have appeared in an orchard? For several reasons, captan should be part of the eradicant fungicide program used against scab. Two pounds per 100 gal. of captan 50W will burn out existing scab and do an excellent job of preventing new infections. This eradicant action is best at temperatures above 80 F.

Benlate, Topsin-M or Syllit have been recommended as eradicants for years. These fungicides are good eradicants, but resistance has made them useless in some parts of the country. There is little apparent resistance in Massachusetts, so any of these materials may be combined with captan or another protectant to improve burn out.

The SI's will also suppress spore development, and help burn out lesions, but they are expensive and don't do a particularly good job protecting apple fruit. When eradicating infections, the interval between sprays should be kept short, at about 7 days. Spray intervals should be kept short, at about 7 days, until lesions stop growing, usually after 2 to 4 applications. They should also be mixed with a protectant fungicide.

For the past couple of weeks, members of the UMass IPM crew have been examining 1500-2000 fruits per day across 48 commercial orchard blocks for evidence of plum curculio activity. In addition to this, we are monitoring on a 3-4 day rotation in several unsprayed sites. In unsprayed trees, egglaying activity began in earnest late last week, reaching 16% damage by Friday (5/15) and increasing to 60% damage by Monday (5/18).

In commercial orchards, damage has been pocketed in traditional hotspots; we have yet to see activity begin to spread throughout monitored areas. What this boils down to, not surprisingly, is that the first, and in some cases the second, PC spray has done a good job of suppressing a moderate immigrating population. This does not mean that we (or they) are completely out of the woods yet.

Data from recent years has shown that while curculio may become active in orchard blocks near bloom, their immigration and egglaying are largely weather driven. With no effective monitoring trap to give an indication of the beginning, end, or peaks of PC activity, we must rely on two other approaches.

First, there is no substitute for continuing to monitor orchard trees for evidence on ongoing PC feeding and egglaying. This allows for a reasonable estimate of the active PC populations present in the orchard; any secondary PC invasions will be evidenced by increases in fresh egglaying and feeding injury between sprays. All told, regular monitoring of fruit for fresh PC injury during the intervals between applications offers a fairly reliable determination of whether or not an additional application is warranted, and whether such application should be a border-row or whole-orchard treatment.

The second method for gauging the progress of PC immigration is the degree-day model developed in Geneva, New York. This model is best used as an indicator of when the PC season is ending, and the specifics of the model will appear in next week's Healthy Fruit.

 

Leafminers Suck Sap

Sap-feeding mines began to appear late last week, and development since then has been quite rapid, given the ideal weather over the past week. Earlier-developing orchards are at the tail end of the ideal timing for use of either Provado or Agrimek against first-generation mines, but areas in which the bulk of the mines are still developing are still within the window for a Provado application.

If no treatment is used against the first-generation mines, we recommend that you continue to monitor buildup of tissue feeding mines in order to estimate the number and timing of the second generation. Treatments against the second generation can be relatively effective, but leafminer development has a tendency to get strung out as the season progresses, making later applications much more difficult to time properly. Thresholds for treatment of the second-generation LM and material recommendations for such a treatment will appear next week.

From pit hardening to early peach fruit are relatively resistant to brown rot. Assuming a good brown rot management program from bloom into shuck splitting and fall, fruit will be free of brown rot and should stay that way as the green fruit enlarges.

A far more critical period occurs when the fruit starts to color and ripen. At that point, consider using the newer SI fungicides labeled against brown rot on peaches: Indar, Elite and Orbit. While these fungicides are pricey, they are also very effective. Indar is particularly effective.

In addition to being very effective, Indar, Elite and Orbit have either a 1 (Indar) or 0 days preharvest interval. The goal of most peach growers in Massachusetts should be to supply as ripe and rot-free a peach as they can.

Healthy Fruit is written by Dan Cooley, Ron Prokopy, Starker Wright, Wes Autio, and Karen Hauschild except where other contributors are noted. Edited by Dan Cooley. Publication is funded in part by the UMass Extension Agroecology Program, grower subscriptions, and the University of Massachusetts IPM Program. Healthy Fruit is available on the Web at The Massachusetts Tree Fruit Advisor, (click here). A text version can be e-mailed to you if you contact me, at dcooley@microbio.umass.edu. Please cite this source if reprinting information.