FruitNet Weekly Report | Publications | Northwest Michigan Horticultural Research Station

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Jim Nugent
District Horticulturist

Nikki Rothwell
District Fruit IPM Agent

Bill Klein
Farm Mgr, NWMHRS

Duke Elsner
Agricultural & Regional Viticulture Agent

Jim Bardenhagen
Leelanau Extension Director

May 23, 2006

Year	2006	2005	2004	2003	2002	16yr. Avg.
GDD42	574	495	438	456	313	468.6
GDD50	265	228	198	204	143	225.9

WEATHER
During the past week weather remained very cool with some continued moisture. Scattered frost occurred on 5/21, 5/22 and 5/23.

GROWTH STAGES at NWMHRS (5/22/06 10:00 am)

Apple: Mac: Late petal fall, Red delicious: Late petal fall

Pear: Bartlett: 6mm fruit

Sweet Cherry: Hedelfingen: 9mm fruit, Gold: 10mm fruit

Tart Cherry: Montmorency: Shuck split; Balaton: Shuck split

Apricot: 15 mm fruit

Plum: NY 12: Early shuck split

Grapes: Chardonnay: 1-3" shoots

TREE FRUIT REPORT

Apple: Over the past two weeks conditions for apple pollination have been very poor. It will be particularly important this year to assess crop potential prior to application of thinners. Even with all the rain, we have seen very little scab in managed orchards. Fireblight has not been an issue in most blocks so far this year, but as temperatures warm and secondary bloom opens, we need to be aware of fireblight infection for the coming days. Growers should check blocks for late bloom and use the fireblight model on Enviroweather to determine infection potential. Oriental fruit moth numbers are down to zero for the week, probably due to cold temperatures. We have been catching codling moth (CM) but only an average of one per trap here at the NWMHRS and five per trap in an unmanaged block. Blocks that do not have exceptionally high overwintering CM populations have not yet had enough flight to establish a biofix. Our adult spotted tentiform leaf miners (STLM) counts are down to an average of 30 per trap.

Cherry: Sweet cherry fruit are exhibiting a lot of frost scars. The major problem with frost scars is that they lead to cracks during the preharvest fruit swell. This in turn increases the potential for brown rot and Alternaria fruit rot. We have not observed cherry leaf spot so far this season, but European brown rot has shown up in most Balaton blocks and a few Montmorency orchards. No plum curculio have been evident in cherry, but with warming temperatures, we expect them to be in sweet and tart cherries in the next few days. Green fruitworm is present in tart blocks, and we have seen black cherry aphids in higher numbers than is typical.

Small Fruit:

Grapes: Cold temperatures resulted in very slow shoot growth during the last week. Chardonnay shoots are still only at 2-4 inches in length, with clusters now showing. There has been no sign of significant cold injury at the NWMHRS and, so far, only limited reports of injury from growers. The predicted warm temperatures should result in rapid shoot growth over the next week, so growers need to get ready for early powdery mildew sprays. Insect activity has been minimal over the last week.

Miscellaneous:

Deer have already begun feeding on young fruit trees. Growers in Benzie County are reporting the highest deer population in years. Repellents are generally most effective if applied prior to first damage, or at least as soon as possible after first damage, to try to alter behavior before they think you are providing a banquet!

IPM REPORT
By Dr. Nikki Rothwell, District IPM Educator

European Brown Rot

This past week was cool and wet, and with open bloom this combination is perfect for European brown rot (EBR) invasion. So far this season, we have seen many EBR infections in Balaton blocks, and we have observed infection in Montmorency. The timing for EBR chemical control is popcorn through bloom, and the chemistry of choice is Indar. If a block is past bloom, there are no chemical control options. However, growers should plan to prune out the infected areas this winter to reduce inoculum in the orchard for next season.

Fireblight Reminder

Temperatures are predicted to warm through this week and into the weekend, and many orchards have secondary bloom opening; this situation is ideal for fireblight infection. Growers need to be aware of fireblight infection potential for the coming days; they should check blocks for late bloom and use the fireblight model on Enviroweather to determine infection potential (www.enviroweather.msu.edu). Remember that because this disease is based on degree HOURS, not degree DAYS, the infection potential can change very quickly, so growers will need to be check the fireblight model on a routine basis until apples have finished blooming.

PRELIMINARY, BUT NOTEWORTHY FIND: EFFICACY OF INSECTICIDES WITH COPPER AND LIME
Nikki Rothwell, District Fruit IPM Educator
Johanna Nugent, Research Technician
Lisa Talbot, Research Technician
Renae Tuller, Research Technician

In recent years, we have documented cherry leaf spot (CLS) resistance to sterol inhibitors (SI’s). We are currently investigating the potential of using copper to control this disease. Based on data from 2004, we have shown copper at a rate of 1.2 lb actual Cu/acre to be highly efficacious against CLS. However, we have also documented copper’s ability to cause phytotoxicity in hot, dry weather. To minimize copper’s phytotoxic effects, we recommend mixing the copper with lime at a rate of 6 lb/acre. In research plots at the NWMHRS, we have shown this combination of copper and lime to control CLS and reduce phytotoxicity.

Although these results are positive, concerns remain about tank-mixing copper and lime with insecticides. Some insecticides are pH-sensitive, and when lime is added to the tank mix, the water’s pH could be altered enough to change the efficacy of the insecticide. Last week, we conducted a study at the NWMHRS to determine if copper plus lime would reduce the effectiveness of four standard cherry insecticides against field-caught plum curculio (PC). Five PC were placed into petri dishes containing each of the following insecticides: Guthion, Imidan, Actara, and Avaunt. We also compared these insecticides with ‘low’ copper and lime (3.75 lb Cu and 3 lb lime) and a ‘high’ copper and lime (7.5 lb Cu and 6 lb lime). All mixtures were allowed to sit in solution for an hour to simulate actual spray time in the orchard. For control purposes, we placed PC into petri dishses with water, lime alone and copper alone. Because Imidan and Guthion are contact poisons, we placed the chemical mixtures on filter paper. Avaunt must be ingested to cause mortality, so we dipped cherries in the chemical blend before placing them into the petri dishes. Actara, a newer insecticide in the class of neonicotinoids, is a contact material when it is first sprayed. After 3-4 days, the compound is absorbed into the plant and there is a reduction in lethal activity, but insects’ ability to oviposit (lay eggs) dramatically declines. Therefore, we used dipped cherries for Actara. The graphs only reflect PC mortality; oviposition measurements will be documented in the next trial.

The following results are preliminary, but there is an important discovery for growers that intend to use a copper/lime and insecticide tank mix for one of their cover sprays. When Imidan is mixed with high and low levels of copper/lime, the insecticide becomes completely ineffective (Figure 2). In other words, lime changes the pH of the water in the ‘spray tank’ so drastically that Imidan loses all of its insecticidal properties. Another word of caution is in the Avaunt trials where the data suggest this material does not cause PC mortality (Figures 1 and 5). Although these weevils were not dead, their functioning was severely reduced, enough to consider them non-threatening as a pest. Although Avaunt is not killing the weevils outright, it does render them incapacitated. We intend to repeat this experiment multiple times throughout the season to verify the results.

Fig 1

Figure 1: Efficacy of insecticides alone against plum curculio

Fig 2

Figure 2: Efficacy of Imidan with high and low copper against plum curculio

Fig 3

Figure 3: Efficacy of Guthion with high and low copper against plum curculio

Fig 4

Figure 4: Efficacy of Actara with high and low copper against plum curculio

Fig 5

Figure 5: Efficacy of Avaunt with high and low copper against plum curculio

Seasonal Evaporation & Precipitation Beginning May 1, 2006, at NWMHRS
Date	Rainfall/wk at NWMHRS (in.)	Rainfall minus 75% of Evaporation	Evap/week (in.)	75% of Evap/week
5/2	0.00	-1.05	1.40	1.05
5/9	0.03	-1.12	1.53	1.15
5/16	2.02	1.51	0.68	0.51
5/23	0.61	-0.21	1.09	0.82

Totals	2.66	-0.87	4.70	3.53

This issue and past issues of the weekly FruitNet report are posted on our website at: http://www.maes.msu.edu/nwmihort/faxnet.htm

ACTUAL AND PREDICTED DEGREE-DAY
ACCUMULATIONS SINCE MARCH 1, 2006

Please send any comments or suggestions regarding this site to:
Bill Klein, kleinw@msu.edu

Last Revised: 5-23-06