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Healthy Fruit 1998 Vol. 6:1

Apr 1, 1998

What Month Did You Say It Is?

You can interpret this any way you want, El Nino, global warming or the normal variation in weather. Any way you look at it, it's strange.

Here are some of the facts. Last year on April 1, we were in the middle of a snowstorm that dumped 1 to 2 feet of snow over Massachusetts. Yesterday, we recorded the first ever 90 F temperature during March in western Massachusetts. We didn't reach the growth stages we now see until April 30, which was more or less normal. We are somwhere between 3 and 4 weeks ahead of normal.

Apples (most cultivars)

Bud Stage

 

Ave. temp. (F) for 10% kill

 

Ave. temp. (F) for 90% kill

Silver Tip

 

12

 

0

Green Tip

 

15

 

5

Half-inch Green

 

20

 

10

Tight Cluster

 

24

 

16

First Full

 

25

 

18

First Pink

 

25

 

20

Full Pink

 

27

 

22

Post Bloom

 

28

 

23

Temperatures have dropped back, leaving us to regroup. What are the implications for frost damage? These are the tables on critical temperatures from Jon Clements at the Virtual Orchard on the web.

McIntosh growth stages for various locations:

  • Ashfield green tip
  • Belchertown 1/4" green
  • Northboro 1/2" green
  • Sterling 1/4" green
  • Wilbraham 1/2" green

Redhaven peaches at the Hort. Research Ctr. are at pink bud. Cherries are at swollen bud.

Peaches (Elberta)

Bud Stage

 

Ave. temp. (F) for 10% kill

 

Ave. temp. (F) for 90% kill

First swelling

 

18

 

1

Calyx green

 

21

 

5

Calyx red

 

23

 

9

First pink

 

25

 

15

First bloom

 

26

 

21

Full bloom

 

27

 

24

Post bloom

 

28

 

25

Time Critical!

  • Be ready to spray for scab now.
  • It's too late for copper in most areas.
  • Oil if you can.
  • Fertilizer should be going on.
  • Plant from here on out.

Skip Copper

Are you still thinking you might want to use copper? First ask yourself the question, how do I feel about risking fruit russett? Copper at 1/4 inch green or later can easily result in russet at harvest. Keith Yoder at the Winchester Expt. Stat. in Virginia has done quite of bit of testing, and shown that even two applications of low rates of copper will russett fruit. Dave Rosenberger in the Hudson Valley has had tests which indicate 1/4 inch green is the absolute latest you can apply copper without risking russett.

You may be tempted to try the bloom rates, which are less than the dormant rates of copper. Weigh this against the potential benefits. You may reduce fire blight pressure in many cases, though not always. You can control scab for a week or so. You may get some nutritional benefits. You may knock out a few ice-nucleating bacteria (the bacteria that increase frost damage) but that is just a theory. On the other hand, copper applied to apples at 1/4 green has a good chance of russetting a significant number of fruit, especially if cool, wet weather follows the application. If you are growing high-quality fresh fruit this doesn't seem to be a risk worth taking.

On the other hand, if you live in the northwest hills and are quick, you can get the benefits of a copper spray without the risk of russett, because you are still at green tip.

Scab Risk

Scab risk comes down to four basic components:

  • the amount of mature inoculum;
  • the susceptibility of the tissue to scab;
  • the size of the tissue;

We can use these risk factors to determine whether or not to make a fungicide application to control scab. Let's look at where we are relative to these factors.

First, the proportion of inoculum which is already fully mature and ready to release is high. I would estimate it is easily over the threshold for the beginning of the season in most areas, based on the direct observations and the temperature model for scab maturity. Of course, most commercial blocks should be in reasonably good shape in terms of the amount of overwintering scab. But where there is scab inoculum, a lot of it is ready to release with the next wetting period, probably today.

Second, the new, rapidly growing tissue is very susceptible to scab. It will remain that way for the next couple of weeks.

Third, there isn't much tissue our, compared to what there will be in around bloom and petal fall. So, there isn't a lot of target out there for the scab spores to hit.

Dave Gadoury, Bob Seem, Arne Stensvand and Stuart Falk of Cornell's Geneva Ag. Expt. Stat. have done all the math for us for an average year, and checked it against real happenings. They took individual risks based on each of the three factors, amount of inoculum, susceptibility of tissue to scab, and the size of the target tissue, and combined them to get a picture of overall scab risk in a typical season. The heaviest risk usually comes during a two week period from early tight cluster through bloom.

Primary scab season has started. Right now, the risk of scab in a typical orchard is low to moderate in Massachusetts. With today's (April 1) rain, we will go have the first infection period of the season. It will need to be treated.

Nutrients for Buds

Clearly, we are progressing into this growing season extremely early. Unfortunately, this timing puts apples at great risk for spring frosts. Little can be done to prevent significant damage if frosts occur. However, it stands to reason that health buds will be less likely to be damaged than weak buds. Therefore, it may be worth considering nutrient sprays as one way to enhance bud health. They may not do any good, but they are relatively inexpensive and may help.

Specifically, consider sprays of urea. Use spray-grade urea (less than 0.25% biuret) at a rate of 3 lbs/100 gallons. The first spray should be applied at tight cluster to pink and the second at petal fall.

Secondly, consider an application of boron prebloom. Use solubor at a rate of 1 lb/100 gallons at tight cluster.

Zinc chelate (EDTA) may also be beneficial at tight cluster at a rate of 1 lb or 1 quart/100 gallons.

It is no guarantee than these nutrient treatments will help improve bud quality and therefore reduce damage from spring frosts, but they are worth trying.

Tarnished Plant Bug

Silver tip was to have been the time to hang white sticky rectangle traps for monitoring of tarnished plant bug. However, with our rapid progression through silver tip and green tip, some may question the use of the monitoring traps. In most cases, the traps are effective up until late pink, so traps deployed before tight cluster will still give a pretty good idea of TPB activity in the orchard. For greatest effectiveness, traps should be hung at knee height (no higher) toward the outside of the canopy, and should be attached to a branch that will support the trap in the wind. The thresholds at which treatment should be considered are given as follows in the 1998 March Message:

Cumulative TPB per trap

Type of Market

 

Silvertip to Tight Cluster

 

Silvertip to Pink

Wholesale

 

3

 

5

Retail

 

5

 

8

Leafminer

Monitoring traps placed now for leafminer are still effective for determination of population densities. Although we recommend that the traps be in place at silvertip or soon after, last year's peak in LM activity was in early May. The highest levels of activity are generally observed from pink to bloom, so trunk traps should still give a good indication of LM abundance. Traps should be stapled firmly at knee height to the south side of the trunk, and we recommend a minimum of 4 traps per 8 -acre block. Thresholds for LM treatment will be included in following issues of Healthy Fruit .

Leaf Curl

I'm sorry, but if you didn't do something by now you have missed the timing. Applications need to be made in the fall, after leaf drop, or in the spring before bud swell. By now, the fungus has established itself where sprays can't get it. If we have a dry spring, then there shouldn't be too much leaf curl pressure, but if it is wet and cool from here on out, there could be problems. There has been increasing inoculum in recent years.

Pear Psylla

With the warm weather over the past week, it is safe to say that adult psylla have been active in most areas of the state. Three materials have proven effective as petal fall treatments for psylla (Agrimek, Provado and Mitac), but pre-bloom oil sprays are best as a first-line defense. Recent studies in Washington have shown that pre-bloom oil treatments alone significantly reduce the ability of psylla to feed or oviposit. Thorough coverage is necessary for oil to be effective, ideally in 2 pre-bloom sprays. If buds are swelling, which may be the case in only the late-developing orchards at this point, a spray of 2% oil is recommended. The later oil treatment should be a 1% spray and should occur after green cluster, but not later than early white bud. Given proper coverage, oil treatments should significantly reduce feeding and egglaying, as well as smother existent eggs.