Investigator/ Collaborators:
WSU Nooksack Watershed IPM Project in collaboration with Best Sulfur Products(Faith Potter), Whatcom Farmers Cooperative(Derek Gavette) and grower cooperators:
Tena Ondeck
Randy Honcoop

Project Description/How was it done?
Sulforix liquid lime sulfur(Best Sulfur Products) was applied by growers with standard spray equipment at different times and rates. Treatments included 1)untreated control, 2) standard timing and rate (3 Gal. Sulforix in 100 GPA water at budbreak), 3)delayed timing and reduced rate (1.5 Gal. Sulforix in 100 GPA water at 2-3" average new shoot growth at wire) and 4) Standard plus Delayed timing(2X). Each treatment was replicated 3 times and treatment plot size was 2-3 post lengths long and 2 rows wide. Experiments were conducted in two Honcoop fields and one Ondeck field both in the Northwood area in Whatcom County.

Evaluations for phytotoxicity were made in late March, late April, and mid-May. Initial yellow rust infection(aecia) was evaluated in the field in late April, and again in mid May. Based on mid-May findings, fruiting laterals were collected from some of the plots by Dr. Pete Bristow, WSU Puyallup plant pathologist to evaluate primary yellow rust incidence(aecia) more accurately. In early September, spur blight and botrytis cane lesions were counted in the field on 50 primocanes from each plot at two of the three field sites.

Results
Phytoxicity: Standard timing caused leaf distortion and burning of leaf margins in only one of the fields. This was due to low gallonage of water(50 GPA) and resulting increased product concentration applied in this field. The field outgrew this initial damage over the next month. The late April evaluation showed that the delayed timing and combined treatments caused a slight to moderate increase in both of these phytotoxic symptoms compared to the standard timing and the untreated plots, but the plants outgrew these symptoms by mid May. There was a subtle stunting of lateral growth and reduced canopy vigor associated with the delayed applications of Sulforix in late April, but this was difficult to see a few weeks later. Late May samples by Bristow confirmed slightly reduced lateral length in delayed treatments but no likely yield effect since the number of flowers/lateral was the same across all treatments.

Diseases: Yellow rust aecia began to appear on fruiting lateral leaves in late April. Field ratings in mid May indicated that aecia infection was significantly lower in the delayed and combined treatments compared to the standard timing and untreated control. Subsequent lab counts from two of the fields confirmed that the delayed and combined Sulforix treatments greatly reduced the incidence of initial yellow rust infection. Standard timing reduced disease incidence when compared to the control but was not as effective as the delayed treatments.

In one field, late summer spur blight infection of primocanes was lower in all Sulforix treatments compared to untreated plots. The delayed and 2x treatments in this field had slightly fewer spur blight lesions compared to the standard timing. In the other field, there was no difference between the untreated and the standard timing. This may be due to the reduced gallonage in this field with the first spray. However spur blight primocane infection was reduced in both the delayed and 2X treatments compared to the standard timing and untreated control.

There was no reduction in botrytis cane lesion infections associated with any of the treatments.

Any problems or limitations?
Secondary yellow rust infections (uridia stage) were not evaluated. It is assumed that the observed reduction in initial infection should have resulted in reduced disease incidence during and after harvest.

What did we learn?
Standard timing of Sulforix at 3 gallon product/acre in 100 GPA is not phytotoxic, but reducing gallonage to 50 GPA, which doubles the concentration, will burn margins of developing leaves. Plants outgrow this damage.

Delayed Sulforix applications at half rate causes increased leaf distortion and burning of leaf margins and temporary stunting of lateral length, but these symptoms are quickly outgrown and yield is not likely reduced. Delayed timing reduces initial yellow rust infection in the spring. Sulforix may be directly toxic to the spur blight pathogen in the spring. Late season spur blight infections on canes were reduced in Sulforix treated plots.