IMPROVE FRUIT ROT CONTROL IN CARRY-OVER STRAWBERRIES

Vegetable Growers News
July - August 2001, Vol. 8, No. 4

Charlie O'Dell, Extension Horticulturist Emeritus
Dept. Horticulture, VA Tech, Blacksburg, VA

The cool, wet spring of 2001 in this area was a fine opportunity for me to evaluate strawberry fungicides on a field of second year carry-over Chandler strawberries. The weather also proved a real challenge to control Anthracnose Fruit Rot as well as Botrytis Gray Mold. These fruit rots concern both matted row producers and growers in colder areas with carry-over plastic mulched hill culture berries.

For this test, second year Chandler plots were selected since they may also carry over more disease inoculum spores even though the raised beds were cleaned off in late February with plastic leaf rakes followed by a leaf blower to remove dead leaves and un-rooted runners. Plots were chosen on an east-facing slope since it warms and dries slowly with weaker afternoon sun, possibly providing better conditions for disease. This cool site also helps extend our harvest season here at home.

Fungicide treatments were applied during bloom from April 29 through May 26 on this site, 4 sprays total. Plots were replicated 4 times and included a control treatment using only water. 1.05 acres were used for these treatments. Before treatments began I was bragging and proud of my sprayer modification: 3 nozzles per bed were crafted so that one spray tip was centered over each bed plus two spray tips were mounted at 45 degree angle on each side of each bed. I was able to drench each bed with 100 lbs. pressure p.s.i. at 120 gallons spray per acre. I thought, "fruit rots won't have a chance", but I did not realize what nature had in store!

Table 1. Fungicide Treatments, Second Year Chandler Plots, Year 2000

Trt. 1.	Elevate 1.0 lbs/A plus Captan 3.0 lbs/A @ 120 gallons water/acre @ 100 psi, (18 gallons/0.15 A)
Trt. 2.	Switch @ 14 oz/A as above
Trt. 3.	Elevate @ 1.5 lbs/acre alt. with Switch @ 14 oz/A as above
Trt. 4.	Elevate @ 1.0 lbs/A plus Thiram 75 WDG @ 3.4 lbs/A as above
Trt. 5.	Captan 50 WP @ 6.0 lbs/A as above
Trt. 6.	Thiram 75 WDG @ 4.4 lbs/A as above
Trt. 7.	Control, no fungicides, water only as above

Table 2. Summary of Treatments Over All Harvests, Weight of Sound Fruit (ounces), Weight of Unsound Fruit (ounces) and Percentage Rot, 0.15 Acre Plots

Trt.	Wt. of Sound	Wt. of Rotten	Total Harvest Wt.	Percent Rot
1.	190.8	80.8	271.6	29.7
2.	143.2	39.6	182.8	21.7
3.	276.3	64.4	340.7	18.9
4.	228.4	75.6	304.0	24.9
5.	251.4	53.6	305.0	17.6
6.	201.2	41.0	242.2	16.9
7.	93.3	67.0	160.2	41.8

Conclusions

While Botrytis Gray Mold Fruit Rot was far more prevalent in the control receiving no fungicides, Gray Mold was easily controlled by all of the fungicide treatments applied during bloom. The primary fruit rot observed and tabulated was Anthracnose ("black spot") Fruit Rot. Never before here in the cooler mountain area have I witnessed any significant degree of Anthracnose Fruit Rot in previous seasons going back over a decade of growing carry-over plastic mulched Chandlers! However, never during the past decade as well, have I witnessed such a cool, wet harvest season as we had this past spring. For example, during the peak of our harvest, we had daily rains for 11 consecutive days that totaled 10.4 inches! We harvested these plots with raincoats and rubber boots right on through this wet period, but area U-Pick berry fields were devastated by this prolonged wet event in their harvest peak. Surely, if all-risk crop insurance is becoming available in our region for horticultural enterprises, our wives in their good sense, should insist that it's illegal to grow strawberries or other high cost, high weather-risk crops without it!

This high amount of Anthracnose Fruit Rot here both surprised us and caught us off-guard this year. Treatments containing higher labeled rates of Captan as well as Thiram showed some degree of suppression of Anthracnose. In hind site, higher rates of Captan and Thiram should have been used in the Elevate tank-mix treatments (Trts. 1 and 4). The combination of Elevate for Gray Mold control plus higher labeled rates of Captan or Thiram for greater activity against Anthracnose would have likely provided broader spectrum fruit rot control in this trial.

The levels of Anthracnose rot in this test in this wet harvest year are very much unacceptable and unprofitable. This test clearly shows us the dire need for a better disease control strategy in the future, needed next year, including labels for use of effective Anthracnose Fruit Rot-fighting fungicides such as Quadris, for all areas! Virginia is not, and has not been on emergency permit labels for Quadris to this point, aarrhh politics! Both Captan and Thiram have been around for many decades and gave good results in this test. Both products would be effective components of a strong resistance management program. Also, alternating Elevate with Switch looks very promising to go along with that future product label for control of Anthracnose Fruit Rot.

Special thanks to Wes Perdue, UCB Chemicals Company, for supplying Thiram fungicide for this test; to Bobby Bassi of Syngenta Chemical Company for supplying Switch fungicide for this test (national label pending for strawberries); and, to Kevin Forney of TomenAgro Corporation for supplying Elevate and Captan fungicides for this test, for helping develop treatment protocols and for the encouragement to conduct this commercial scale test on our farm.

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