Evaluation of Products to Control Phytophthora Crown rot in annual strawberry, 2015-2016
University of Florida, IFAS
Gulf Coast Research and Education Center
L. Cordova, J. Mertely, and N.A.Peres
Wimauma, FL 33598

STRAWBERRY (Fragaria x ananassa ‘Florida 127’)
Phytophthora crown rot; Phytophthora cactorum

Objective: The purpose of this rial was to compare the efficacy of two phosphite products, chemical fungicides and organic soil supplements for the control of crown rot on strawberries.
Method: Oct 2015, bare-root runner plants from Canada were transplanted into plastic-mulched beds fumigated with Telone C-35 at 27 gal/A. The beds were 32-in. wide at the base on 4-ft centers. Each bed had two staggered rows of plants spaced 12 in. apart with 12-in. in-row plant spacing. Treatments were arranged in a randomized complete block design with four blocks in adjacent beds. Plots consisted of 22 plants in 10.5 ft of bed separated by 3- to 4-ft gaps between plots. Plants were inoculated by dipping the roots in a suspension of 1 x 104 zoospores/ml of P. cactorum just before planting. Both inoculated and non-inoculated controls were included in the experimental design. After transplant, beds were irrigated by overhead sprinklers during the day for 10 days to facilitate establishment, then irrigated and fertilized through a central drip tape. Chemigation treatments were applied in 0.4 gal water per foot of bed (4,630 gal/A) through twin dedicated drip-tapes in each plot. Each tape was placed next to a row of plants, and was 12-ft long with 12-in. emitter spacing. Pre-plant applications of biological products were made 3 d before planting. All other applications were made from 22 Oct (2 weeks after planting) to 3 Dec (8 WAP). Foliar applications were made with a CO2-powered sprayers at 60 psi and 100 gal/A. The spray wands were equipped with two TeeJet® hollow-cone nozzles spaced 12 in. apart. Plants were evaluated for disease every 2 wk from 9 Nov (4 WAP) to 1 Feb (16 WAP). Plants that were dead, partially wilted, or severely stunted were considered diseased.
Results: When the first disease assessment was made 4 WAP, 18.9 % of all plants in the trial were diseased (data not shown). Six additional assessments were made at 2-wk intervals. With each successive assessment, an additional 10 -20% of the plants became diseased, based on the number of healthy plants at the start of the interval. This relatively uniform disease progress may be related to unusually warm weather in Nov and Dec 2015. Normally, losses tend to be high early in the season, and lower with the onset of cool weather in Dec. and Jan. At 10 WAP, disease incidence was 41.2% in the inoculated control compared to 4.6% in the non-inoculated control. Most treatments ranged between these two extremes. Nevertheless, there was no significant difference in disease incidence at this time. By 16 WAP, treatment effects were significant, but only the inoculated and non-inoculated controls showed significant differences in disease incidence. During the post application period from 10 to 16 WAP, no treatment significantly reduced disease, but surprisingly, disease incidence was higher in the Ranman and TerraGrow/TerraClean treatments than in the inoculated control. Although significant reductions in disease incidence were not demonstrated, Ridomil Gold alone and TKO (a potassium phosphite product) significantly increased marketable yield, whereas K-Phite (a similar phosphite product applied at equivalent rate of active ingredient) did not.


Marketable Fruit Yield
Pounds per Acre Harvested


strawberry_research

Phytophthora Strawberry Trial, 2015-2016
Rate 2 quarts per acre every 2 weeks.
University of Florida, Gulf Coast Research and Education Center, Wimauma, FL



Phytophthora Incidence on Strawberry
% of diseased plants


strawberry_research

Phytophthora Strawberry Trial, 2015-2016
Rate 2 quarts per acre every 2 weeks.
University of Florida, Gulf Coast Research and Education Center, Wimauma, FL