Gordon Johnson, Retired Extension Specialist; email@example.com
The following are strawberry diseases to watch for starting in the fall that can cause plant collapse. This information was adapted from Disease management recommendations for fall-planted strawberry plug plants by Kathy Demchak, Penn State Extension and Dr. Mengjun Hu, University of Maryland.
Phytophthora Crown Rot
This disease has caused severe losses in some varieties.
Symptoms consist of complete plant collapse in the fall and/or spring. Collapsing plants show a reddish-brown discoloration to the crown that is sharply delineated from healthy tissue, though eventually the entire crown may be affected.
Plant collapse and bluish-green leaf color of ‘Flavorfest’ plants affected by Phytophthora crown rot.
Historically, this disease has been caused by specific “pathotypes” of Phytophthora cactorum which differ from the ones causing leather rot and red stele (Phytophthora root rot)
Darkened tissue is usually at the top of the crown but may appear in other areas or be more limited in scope, depending on the entry point of the fungus and length of time since initial infection.
Some varieties such as Camarosa have good resistance. With varieties susceptible to Phytophthora cactorum such as “Flavorfest”, use fields that have never been used for growing strawberries if possible. At planting, use a plant dip of fosetyl-Al (Aliette WDG) or a phosphite product (ProPhyt, Phostrol, etc.). Make foliar applications through mid-Fall at intervals allowed on the label. The fungus is thought to become inactive later in the fall when temperatures cool. Watch for symptoms next spring and continue to treat.
Anthracnose Crown Rot
With this disease, plants fail to grow as expected, and may eventually die. Upon close examination, you may find that the main crown has died, but branch crowns have started to grow. No cultivars are completely, but some such as Chandler are very susceptible. Affected crowns appear firm and reddish brown when they are sliced open. Crown tissue may be uniformly discolored brown, and symptoms sometimes can be confused with those from other crown rot issues.
Switch and Abound plant dips have been found to help with anthracnose crown rot control. Refer to the label for instructions. Two or three applications of captan or thiram may be made after planting during the fall season at 10- to 14-day intervals. Other products are also labeled for this use including Tilt, Inspire Super, Quadris Top, Quilt Xcel, Luna Sensation, Merivon Xemium, Pristine, Miravis Prime, Switch, Abound, Cabrio and Aftershock.
Neopestalotiopsis Crown and Fruit Rot
This relatively new disease can also cause plant losses.
There are various strains or species of Neopestalotiopsis that cause different symptoms ranging from slowly progressing foliar symptoms to rapid plant decline and death. Early symptoms appear on leaves and consist of tan to brown roughly V-shaped lesions that are wider at the edge of the leaf. If the more virulent strain is present, large areas of the leaf are invaded in a matter of a few days with pycnidia (tiny black raised dots) appearing in the lesions shortly thereafter. The disease can also invade the crown and kill plants and causes a fruit rot similar to anthracnose fruit rot.
Many cultivars seem to be susceptible. At planting and throughout the fall, remove any leaves showing disease symptoms. Sprays of Thiram, Switch, or Miravis Prime, 7 to 10 days apart can reduce the disease. Other materials showed little efficacy against this disease. There may be a correlation between spider mites and high severity of Neopestalotiopsis. A miticide spray may therefore be important to managing this disease.
Neopestalotiopsis on ‘Galletta’ showing V-shaped lesion which has consumed most of the leaf within a few days.
Angular Leaf Spot
This is a bacterial disease that is usually noticed in the spring because it causes caps to turn brown but is mentioned here because if the infection is severe enough, the bacteria can invade the plants’ vascular systems causing them to collapse, and thus could be confused with other causes of plant collapse. The bacteria are splashed around by water and unlike most other diseases, this one thrives under cold temperatures. In years where long periods of overhead irrigation for frost protection are needed, it can become very widespread, resulting in tissue death that could be mistaken for fungal diseases.
The most obvious symptom of angular leaf spot is blackened berry caps.
The bacteria also cause clearing of leaf tissue, at first delineated by the leaf veins. Injured tissue eventually coalesces and may die.
Some newer cultivars grown in plasticulture appear to be quite susceptible. Since this disease is caused by a bacterium and not a fungus, copper-based materials are needed instead of standard fungicides (which have no effect) and should be applied in the spring to protect healthy foliage and berry caps from disease spread. Make these applications only if the disease is known to be present, as phytotoxicity can occur with multiple applications and when drying conditions are prolonged. It is unlikely that any spray applications will be needed for this disease in the fall. In addition, Actigard, which induces the plants’ systemic activated resistance, provided some control efficacy based on trials. Note that Actigard should be applied at the lowest label rate. Higher rates were found to reduce yields.