Holly Diseases
Gary W. Moorman, Professor of Plant Pathology
| Disease | Syptoms | Pathogen/Cause | Management |
|---|---|---|---|
| Leaf scorch | Circular to irregular, tan spots appear in early spring or summer. Tiny, black fungal fruiting structures pepper the spot surface as a result of attack by a secondary fungus. | Young leaves formed during cool, damp weather are damaged easily if exposed to hot, dry, windy weather. | No control is recommended. |
| Nematodes | Yellowing, stunting, and twig dieback occur. The root system is small and has dead areas, as well as galls in some cases. | Criconemella, Meloidogyne, Pratylenchus, or Tylenchorhynchus | An analysis of soil and roots must be done to confirm that nematodes are actually causing the symptoms. Care for plants well so that they are not under stress from other factors. If the shrub is replaced, first fumigate and thoroughly aerate the soil. |
| Phytophthora root rot | Leaves yellow and brown spots develop. Branches and eventually the entire plant dies. | Phytophthora cinnamomi | Remove the infected plant. Do not replace it with a woody ornamental unless the planting site is first fumigated and aerated thoroughly. Protect surrounding plants with mefenoxam, etridiazole, or fosetyl-Al. |
| Spine spot | Pinhead-sized or larger spots frequently surrounded by a purple halo appear on leaves in late winter and early spring. | Once thought to be caused by the sharp points of leaves puncturing each other, spine spot is now known to be caused by the ovipositing of certain insects. | No control is recommended. |
| Tar spot | Small, yellow spots form on leaves and turn reddish brown with a small, yellow halo later in the summer. In the autumn, a flat black, cushion-shaped fungal structure forms beneath the leaf surface. | Rhytisma prini | No control is recommended. |
| Thielaviopsis root rot | Plants are stunted and have branch dieback. Roots are blackened. | Thielaviopsis | Inspect the roots of containerized hollies before planting. Do not use those with blackened roots. Apply thiophanate methyl, triflumizole, or thiophanate methyl + etridiazole as a soil drench to protect healthy roots. |
Thielaviopsis spores Holly dieback due to Phytophthora root rot in a root cell.
Active Ingredients and Trade Names of the Chemicals
| FRAC Group no. | Risk Level | Class | Active ingredient | REI Restricted Entry Interval | Trade names (EPA Reg. no.) |
|---|---|---|---|---|---|
| 1 | 3 | Benzimidazole | thiophanate methyl | 12 | 3336 (1001-69), OHP 6672 (51036-329-59807), Fungo Flo (51036-329-59807), Systec 1998 (48234-12) |
| 3 | 2 | Imidazole | triflumizole | 12 | Terraguard (400-433) |
| 4 | 3 | Acylanine | mefenoxam | 0 | Subdue MAXX (100-796) |
| 14 | 1 | Thiadiazole | etridiazole | 12 | Truban (58185-7), Terrazole (400-416) |
| U | 1 | Phosphonate | fosetyl-Al | 12 | Aliette (432-890) |
| Combined products | 1 | ||||
| 1 + M | thiophanate methyl + etridiazole | Banrot (58185-10) |
Fungicides and Fungicide Resistance Management - Certain fungicides, usually systemic fungicides, are said to be 'at risk' to the development of resistance if they are used repeatedly. See the Risk Level in the above table (1 = low risk; 3 = high risk). The Fungicide Resistance Action Committee has developed a numbering system in which chemicals with the same FRAC Group number have the same mode of action (See http://www.frac.info/frac/index.htm ). It is recommended that chemicals at high risk be used sparingly and in rotation or mixed with chemicals with different modes of actions (different FRAC number).
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Notice: The user of this information assumes all risks for personal injury or property damage.
Warning! Pesticides are poisonous. Read and follow all directions and safety precautions on labels. Handle carefully and store in original labeled containers out of the reach of children, pets, and livestock. Dispose of empty containers right away, in a safe manner and place. Do not contaminate forage, streams or ponds.
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