Northern Michigan FRUITNET'99
The evaporation rate slowed to 1.37" during the past week. For irrigation scheduling this implies the need for approximately 1.03" of moisture for the week. While we measured precipitation on five days last week, the total at the NWMHRS was only 0.81".
GDD 50: 657; GDD 42: 1139
Apricot: Harcot – 26mm
Apples are sizing well with the warm temperatures that we had until recently. Most growers have sprayed for coding moth, with light pressure blocks being the exception. Plum curculio remains active, however, it is past its peak. Spotted tentiform leafminer has started its second generation adult flight. Provado applied in approximately 2 weeks will control this generation, as well as white apple leafhoppper and green apple aphids. Potato leafhoppers are very active in young apples; control can be obtained with Guthion or Imidan. Symptoms of fireblight appeared in some orchards last week. In blocks with only occasional strikes they can be broken out, but if there are many strikes you may end up making matters worse by trying to cut them out. Potato leafhoppers should be controlled in these blocks, as they can spread fireblight.
Sweet cherries are taking on color, and as a result they are much more susceptible to brown rot. Indar, Elite, Orbit or Rovral should be used on a protectant basis until harvest. It is common to find some leaf spot showing up in tart cherries. Spray schedules should be tightened where it is found. Greater peach tree borer and lesser peach tree borer are both flying now, while American plum borer flight is winding down for this generation. Temperatures are too cool for gibb applications; growers who still want to apply would be better off waiting until it warms up to above 70 degrees.
Peaches and apricots injured by tarnished plant bugs have the typical sap oozing symptom now. Thinning should be wrapping up. Rose chafers are common.
We are starting to see bloom on most varieties of grapes. Some potato leafhopper injury is now evident. Rose chafer adults are now active in vineyards, but we have had no reports of high populations causing problems. Vineyard edges, in particular, should be watched closely. It is time for growers to be on the lookout for larvae of the larger sphinx moths, which can severely defoliate young vines. Grape berry moth trap catches averaged 4.3 per trap at the NWMHRS, down slightly from last week. A prebloom fungicide for controlling powdery mildew, black rot and downy mildew is an important spray for good control.
Strawberry harvest began late last week, about 5-6 days later than last year, but still well ahead of normal.
Improving Return Bloom
Scoring apple tree trunks to induce improved return bloom should be done at this time. If scoring young trees to induce flowering, I suggest using a linoleum knife. As trees get larger, then a wider cut is necessary. A hacksaw blade width works well for mature sized trees. Mature trees may be treated with a narrow pruning saw cut. I have seen a chain saw used on large trees to make the scoring cut. The wider the cut, the more severely the tree is affected. Generally, scoring is done with two half circle cuts spaced an inch or two apart.
The mullein bug, Campylomma verbasci, is an important pest of Red Delicious and Spartan apples in Ontario, but it is fairly rare in Michigan. The mullein bug feeds mostly on the weed, common mullein and on apple. Mullein weed appears to be particularly common in young orchards in NW Michigan. Recently a planting of Red Delicious has shown injury from this pest in NW Michigan. The injury shows up on young fruit as slightly reddish pimples, and as the apples grow, the pimples distort the fruit. Fruit with multiple stings often fall off. In addition to Red Delicious and Spartan, Northern Spy, Empire, Cortland, Gala, Jonagold and Golden Delicious are susceptible to injury.
Nymphs hatch out during the bloom and petal fall periods. Like the tarnished plant bug, the mullein bug also has piercing-sucking mouth parts. The nymphs feed on sap from leaves and also sting the developing fruit. After feeding for several weeks the nymphs begin feeding on mites. Once they enter the adult stage they migrate to common mullein, where they feed for the remainder of the summer. In the fall eggs are laid back into apple shoots.
Control can be obtained with an early petal fall spray of Provado or a pyrethroid. Caution: a pyrethroid at this timing is very disrupting to predators.
Gibberellic Acid in Cooler
There is still some gibberellic acid that is being applied to tart cherries. Even though the window for application is almost closed, with predicted high temperatures being only in the upper 50's and lower 60's, I suggest waiting on the gib until warmer weather arrives. Gibberellic acid applied under these very cool conditions typically has a very poor response.
Ethephon Use On Cherries
Ethephon used properly will facilitate mechanical harvesting, but it is important to avoid tree injury. Research and grower experience have shown that lower rates can be used than was first thought. This is caused in part because ethephon’s activity increases as it is applied in higher concentrations, while the original research was conducted on a dilute basis. Lower rates will reduce the likelihood for tree injury.
The activity of the ethephon is greatly influenced by the temperatures that occur during the first 72 hours after application. This creates a challenge to achieve the desired results without experiencing injury. Consider the following:
2) Do not apply when temperatures are below 60 degrees F as activity is greatly reduced.
5) With light sweet cherries, do not apply until fruit on the interior of tree is developing yellow ground color. Ethephon applied prior to this stage of development may cause fruit to drop prematurely with stems attached.
6) Consider the size of the trees when determining the appropriate rate per acre for concentrate spraying. Rates are based on typical full size trees. When treating younger blocks with smaller tree size, adjust the rate per acre downward.
7) Ethephon is applied 8-14 days prior to anticipated harvest. The time required to achieve adequate loosening is a function of ethephon rate and temperature.
8) Do not harvest cherries within 7 days of application of ethephon (7 day PHI on label).
10) Questions always arise about tank mixing ethephon. While there is no research data regarding tank-mixing ethephon, according to experience there appears to be no problem tank mixing ethephon with the fungicides and insecticides commonly used at this time. However, it is possible that materials in the tank may act as a buffer to the ethephon thereby causing some loss in activity. This could be overcome by acidifying the tank mixture prior to the ethephon being added. Do not tank mix with foliar nutrients or compounds such as crack inhibitors, bird repellents, etc. Avoid the use of surfactants unless prior experience has indicated their effect on the ethephon.
11) Ethephon has a 48-hour worker protection re-entry interval (REI).
1. Light Varieties
B. When applied dilute, use no more than the full rate of 1 pt/100 gallons.
B. When applied dilute, use no more than the full rate of 1 1/3 pts/100 gallons.
B. When applied dilute,
apply no more than 1/3 pint/100 gal.
Under certain conditions,
ethephon may promote softening of tart cherries. This seems to
be most apt to occur when a period of extended cool weather follows
the application of ethephon. It may be possible to minimize
this effect by delaying application during exceptionally cool
weather until closer to anticipated harvest, then using a relatively
higher ethephon rate, thereby shortening the time cherries are
exposed to ethephon, but this technique has not been researched.
Insect Trap Count Averages - 1999
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