Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 26, 1996
Publication Date: N/A
Interpretive Summary: Fungicides must be applied to pecan orchards starting at bud break, about April 1, and continued at 2 week intervals through mid May. Three fungicides available for application during this period are propiconazole (Orbit), fenbuconazole (Enable) and fentin hydroxide (SuperTin). Zinc sprays are also applied to the pecan orchard to reduce zinc deficiency of the foliage during this time, either alone or as a tank mix with the fungicides. The effects of the fungicides and zinc on pollination, fruit set and tree physiology are not fully known; however, reduced pollen germination and deformed stigmatic surface were attributed to fentin hydroxide and reduced leaf area to propiconazole. There was no effect on fruit set of Desirable pecan when zinc or the fungicides were applied alone or in combination either 5 days prior to, during or 5 days after stigma receptivity. Neither fenbuconazole nor fentin hydroxide had any effect on leaf area of greenhouse grown pecan seedlings but propiconazole significantly reduced seedling leaf area. Reduced leaf area was not detected on 3 cultivars, Pawnee, Cheyenne and Desirable, when the fungicides were applied in the orchard. The 3 fungicides protected pecan fruit from pecan scab disease equally, as measured by nut weight. These data indicate that the 3 fungicides effectively control pecan scab, are compatible with zinc applications, and have no detrimental effect on leaf area or fruit set under orchard conditions.
Technical Abstract: Propiconazole suppressed leaf area of a wide variety of young pecan [Carya illinoinensis (Wangenh.) K. Koch] seedling genotypes but did not reduce leaf area of trees in commercial orchards. Leaf area declined linearly as dosage increased from 0 to 473 ml/378.5 liter (0 to 16 oz/100 gal). Suppression of leaf area by propiconazole was inversely proportional to leaf age. No reduction of leaf area was detected in orchards where Cheyenne, Desirable and Pawnee were treated with 3 applications (14 day intervals) of fungicide (either propiconazole, fentin hydroxide or fenbuconazole) from bud break to early May. Spring application of the 3 fungicides alone or in combination with zinc did not influence fruit set. Control of pecan scab [Cladosporium caryigenum (Ell. et Lang) Gottwald] was achieved with fentin hydroxide or fenbuconazole for the full season or with propiconazole used early season followed by fentin hydroxide for late season disease control. There was no difference among fungicide treatments on nut weight. These data indicate that pecan fungicides applied during pollination at recommended dosages and intervals, with or without zinc, do not adversely influence leaf area or fruit set of orchard trees.