Cause A fungus, Ophiognomonia leptostyla. The disease has caused severe defoliation, especially in the 'Adams' variety. The fungus overwinters in old infected leaves and nuts on the ground and in cankers on twigs of the past year's growth. During spring rains, spores (ascospores) are forcibly ejected from fruiting bodies (perithecia), which develop in the old diseased leaves and nuts, and are blown to new growth where they induce primary infection. Spores produced in acervuli in old twig lesions are also a source of primary infection. Successive generations of summer spores borne in primary and secondary lesions subsequently spread the disease.
Symptoms On leaves, many circular to irregularly circular reddish-brown to grayish-brown spots 0.0625 to 0.75 inch in diameter. On stems of shoots of current-season growth, lesions are oval to irregularly circular, sunken, light grayish-brown dead areas with dark reddish-brown margins. Summer fruiting bodies (acervuli) of the fungus are generally borne in abundance on twig lesions. The disease is most serious and destructive on nuts; in the husk it causes depressed circular to irregularly circular dead spots, not quite as large as those on leaves. If the nut is infected very young, it does not develop normally and often drops to the ground prematurely. Severe disease may seriously reduce yield.
Cultural control
- Rake and destroy fallen leaves and nuts.
- Prune off infected twigs and branches, if practical.
- Maintain adequate nitrogen fertility.
Chemical control Many of these chemicals have received registration for the nut-crop group, may be efficacious and are legal to use on walnut, however, most have not been tested for efficacy against anthracnose. Tank-mix or alternate chemicals to prevent fungi from developing resistance. Limit the use of any one group during crop production.
- Abound at 12 fl oz/A. Do not use within 45 days of harvest or with silicone-based surfactants. Sprayers should not be used on apples. Group 11 fungicide. 4-hr reentry.
- Aproach at 6 to 12 fl oz/A plus a surfactant. Do not use more than 3 applications, on trees less than 2-years old or within 7 days of harvest. Group 11 fungicide. 12-hr reentry.
- Bordeaux 4-2-100. Group M1 fungicide. O
- Cevya at 4 to 5 fl oz/A. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
- Copper hydroxide materials are not specifically registered for this disease but are registered for walnuts and have been effective. Group M1 fungicides. O
- Champ WG at 4 to 8 lb/A. 48-hr reentry.
- Kocide 3000 at 3.5 to 7 lb/A. 48-hr reentry.
- Nu-Cop 50 DF at 4 to 8 lb/A. 48-hr reentry.
- Dodine FL at 3 pints/A. Spray when leaves first unfold and repeat at 10- to 14-day intervals. Do not use within 7 days of harvest. Group U12 fungicide. 48-hr reentry.
- Flint Extra at 3 to 3.8 oz/A. Do not apply within 60 days of harvest. Group 11 fungicide. 12-hr reentry.
- Inspire Super at 16 to 20 fl oz/A. Do not apply within 14 days of harvest. Group 3 + 9 fungicide. 12-hr reentry.
- Luna Experience at 10 to 17 fl oz/A. Do not use within 35 days of harvest. Group 3 + 7 fungicide. 12-hr reentry.
- Luna Sensation at 5 to 7.6 fl oz/A. Do not use within 14 days of harvest. Group 7 + 11 fungicide. 12-hr reentry.
- Merivon at 5 to 6.5 fl oz/A. Do not use with EC or oil-based products. Do not use within 14 days of harvest. Group 7 + 11 fungicide. 12-hr reentry.
- Miravis Prime at 9.1 fl oz/A. Do not use within 14 days of harvest. Group 7 + 12 fungicide. 12-hr reentry.
- Pristine at 10.5 to 14.5 oz/A. Do not use within 14 days of harvest. Group 7 + 11 fungicide. 12-hr reentry.
- Propiconazole-based fungicides are registered. Do not apply within 60 days of harvest. Group 3 fungicides.
- Bumper 41.8 EC at 4 to 8 fl oz/A. 12-hr reentry.
- Propi-Max EC at 4 to 8 fl oz/A. 12-hr reentry.
- Tilt at 4 to 8 fl oz/A. 24-hr reentry.
- Quadris at 12 fl oz/A. Do not use within 45 days of harvest or with silicone-based surfactants. Sprayers should not be used on apples. Group 11 fungicide. 4-hr reentry.
- Quadris Top at 12 to 14 fl oz/A. Do not use within 45 days of harvest. Group 3 + 11 fungicide. 12-hr reentry.
- Quash at 3.5 oz/A. Do not use within 25 days of harvest. Group 3 fungicide. 12-hr reentry.
- QuiltXcel at 14 to 21 fl oz/A. Do not use within 60 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
- Regev at 4 to 8.5 fl oz/A. Do not apply within 14 days of harvest. Group 3 + BM01 fungicides. 12-hr reentry.
- Rhyme at 7 fl oz/A. Do not use within 14 days of harvest. Group 3 fungicide. 12-hr reentry.
- Syllit FL at 3 pints/A. Spray when leaves first unfold and repeat at 10- to 14-day intervals. Do not use within 7 days of harvest. Group U12 fungicide. 48-hr reentry.
- Tesaris at 3.4 to 5.7 fl oz/A. Do not use with oil based products or within 14 days of harvest. Group 7 fungicide. 12-hr reentry.
- TopGuard at 7 to 14 fl oz/A. Do not use within 7 days of harvest. Group 3 fungicide. 12-hr reentry.
- Topguard EQ at 5 to 8 fl oz/A. Do not use with silicone surfactants or within 45 days of harvest. Sprayers should not be used on apples. Group 3 + 11 fungicide. 12-hr reentry.
Chemical control For nonbearing nursery and landscape plantings.
- Banner MAXX at 8.5 fl oz/100 gal water. For nonbearing nursery and landscape plantings only. Group 3 fungicide. 12-hr reentry.
- Mancozeb-based products. Not for food or feed purposes. Only for nursery-grown ornamental trees. Group M3 fungicides. 24-hr reentry.
- Fore 80 WP at 1.5 lb/100 gal water plus a spreader-sticker.
- Protect DF at 1 to 2 lb/100 gal water plus 2 to 4 oz spreader-sticker.
References Berry, F.H. 1977. Control of walnut anthracnose with fungicides in a black walnut plantation. Plant Disease Reporter 61:378-379.
Miller, P.W., Schuster, C.E., and Stephenson, R.E. 1945. Diseases of the Walnuts in the Pacific Northwest and Their Control. USDA and Oregon State University. OSU Agricultural Experiment Station Bulletin 435.