1999 Cranberry Fungicide Field Trials—Wisconsin

Patricia McManus, Dana Bauman, and Rick Voland

Fungicide efficacy testing for cottonball and cranberry field rots were conducted at one site in Cranmoor township west of Wisconsin Rapids, WI. This approximately 30 yr-old Searles bed had a high incidence of cottonball and other fruit rots in 1998. Plots were 1.5 m² with 0.5 m alleys separating plots. Fungicides were applied in the equivalent of 50 gallon/acre (1.5 L per 8 reps of a treatment) at 40 psi pressure. Treatments (Table 1) were randomized in each of 8 blocks (repetitions). Fungicides were applied either in the morning (before 9 a.m.) or in the evening, and weather conditions were calm (Table 2).

Cottonball (Monilinia oxycocci)

Focus was on the sterol demethylation inhibitors (Orbit and Indar) and "reduced risk" compounds (Abound, CGA279, and BAS500). The Orbit 4-spray schedule was compared to the 2-spray schedule to follow up on previous research. A second goal was to see if "field rot" fungicides (Bravo and Dithane) are useful against cottonball.

Field rots (disease complex caused by numerous fungi)

Focus was on optimizing the timing of currently available compounds (e.g., is bloom spray more effective than post bloom). An additional goal was to evaluate the "cottonball" fungicides for control of field rot.

Cottonball disease ratings included primary infection (data collected on June 18) and secondary infection just prior to commercial harvest (data collected on September 21). Field rot disease ratings were done at the same time as secondary cottonball rating. Other data collected included fruit set, yield, color, and individual berry weight. Data were analyzed using SAS statistical software.

Results are presented in Table 3. Cottonball disease pressure was relatively low. None of the fungicide treatments had a significant impact on primary cottonball (tip blight), which is consistent with our previous findings under low disease pressure conditions. Fungicides also had no effect on field rot incidence. Treatments 1-6 (sterol demethylation inhibitors and strobilurins), which were specifically aimed at cottonball, all reduced secondary cottonball compared to the untreated control. Consistent with previous findings, Orbit applied only during bloom was as effective as Orbit applied during shoot elongation and bloom. Treatments 8 and 9 (3 sprays of Bravo or CGA279202 starting during bloom) were intended as field rot sprays but controlled cottonball. However, Dithane and BAS500 on the same 3-spray schedule did not control cottonball. Field rot sprays of Dithane and Bravo (treatments 11 and 12) started during late bloom also did not control cottonball. Fruit set was reduced when Bravo was applied starting at early bloom (treatment 8), which is consistent with Jeffers’ findings in the late 1980s and observations of some growers. But despite the reduction in fruit set, yield was not reduced. The two Dithane programs (treatments 7 and 11) reduced color significantly compared to the control.

Table 2. Weather conditions during fungicide application.