STRAWBERRY

STRAWBERRY (Fragaria x ananassa ‘Camarosa’) J. C. Mertely and T. E. Seijo

Powdery mildew; Sphaerotheca macularis University of Florida, GCREC

13138 Lewis Gallagher Road

Dover, FL 33527

Evaluation of fungicides to control powdery mildew on annual strawberry, 2002-03.

Bare root plants from Canada were transplanted into methyl bromide:chloropicrin (67:33) fumigated soil in plastic mulched raised beds on 24 Oct 02. The transplants were irrigated by overhead sprinkler for 10 days to facilitate establishment, then irrigated and fertilized through drip tape. The experiment was conducted in four adjacent beds (28 in wide on 4-ft centers) enclosed in a large plastic tunnel on 26 Nov. The treatments were arranged in a randomized complete block design with four blocks, each in a separate bed. The plots were 6.9 ft long and contained a total of 10 plants in two staggered rows in a bed. Fungicide treatments were applied with a CO₂ backpack sprayer calibrated to deliver 100 gal/acre at 40 psi. Treatments were applied on 7- or 14-day schedules over an 18-wk period from 13 Nov through 12 Mar. Fruit were harvested twice weekly from 10 Jan to 11 Mar (18 harvests). Marketable fruit were counted and weighed. Total numbers of unmarketable fruit, and all fruit showing conspicuous growth of Sphaerotheca macularis on the achenes, were also enumerated. The incidence of diseased fruit (number of fruit with powdery mildew divided by total number of marketable and unmarketable fruit, expressed in percent) and total marketable yield (lb/A) are reported. Disease incidence data were transformed (arcsine square root) before analysis. Data were analyzed by ANOVA and treatment means separated by Fisher’s protected LSD (P £ 0.05). Untransformed values are presented in the table.

The 2002-03 strawberry season was characterized by an unusually warm Oct and an unusually cold Jan. Little powdery mildew developed on strawberry foliage during this experiment. The tunnel may have been erected too late in the season to facilitate foliar infection. However, conditions were favorable for fruit infection. Significant treatment differences in marketable yields and incidence of powdery mildew on the fruit were found. Disease incidence was reduced by all treatments, but A1639, Quintec, and sulfur treatments provided better control than the Nova and Procure treatments. Weekly applications of A1639 (Crompton Uniroyal, Middlebury, CT) at 1.78 oz produced the highest yield of marketable fruit; however A1639 at 3.57 oz and two Quintec treatments produced statistically equivalent results.

Treatment, rate/acre and schedule (days between applications)	Powdery mildew incidence (%)^z		Marketable yield (lbs/acre)
A1639, 10WDG, 3.57 oz, 7 day..........................................................................................	0.1	a^y	14,300	ab
A1639, 10WDG, 1.78 oz, 7 day..........................................................................................	0.3	a	15,500	a
Procure 50WS, 4 oz, 14 day, alternating with sulfur 6L, 6.5 pt, 14 day.......................	0.3	a	11,400	c
Sulfur 6L, 6.5 pt, 14 day......................................................................................................	0.5	a	11,800	bc
Quintec 250SC, 4 oz, 14 day..............................................................................................	1.0	a	12,900	abc
Quintec 250SC, 4 oz, 14 day, alternating with Nova 40W, 5 oz, 14 day	1.3	a	12,900	abc
Procure 480SC, 4 oz, 7 day.................................................................................................	5.2	b	12,400	bc
Procure 50WS, 4 oz, 7 day.................................................................................................	5.9	b	12,400	bc
Nova 40W, 5 oz, 14 day.....................................................................................................	6.6	b	12,100	bc
Untreated check .................................................................................................................	15.7	c	10,300	c

^zNumber of fruit with conspicuous powdery mildew growth on achenes divided by total number of marketable and unmarketable fruit, expressed as a percent.
^yTreatment means within a column followed by the same letter are not significantly different according to Fisher’s protected LSD (P £ 0.05).