The Final Fungicide Application – Vegetable Crops Hotline

The Final Fungicide Application

Vegetable growers may be wondering when to apply the final fungicide application. It is important to leave the crop protected until the last harvest. Yet, it is important not to waste fungicides.

In most cases, the last fungicide application should occur 10 to 14 days from the final harvest. Most fungicides that are designed to protect the foliage will last on or in the plant for 10 to 14 days. In addition, foliar diseases that affect primarily leaves and stems such as downy mildew, early blight, gummy stem blight/black rot, powdery mildew, and Septoria leaf spot that do not affect fruit directly are not necessary a few days from harvest. A fungicide application a few days before harvest is expensive and ineffective. Plus, it is necessary to keep in mind the Pre-Harvest Interval (PHI). Note—downy mildew has not been reported in Indiana in 2022.

Some diseases affect the fruit directly. However, even for these diseases, most final fungicide applications should occur no sooner than 7 days before harvest. Lesions of diseases that occur directly on the fruit usually result from splash from the foliage. Therefore, season-long protection of the foliage is important for protecting the fruit.

Diseases that may affect fruit directly include:

Cucurbits-anthracnose (cantaloupe/watermelon), bacterial spot (pumpkin) Plectosporium blight (pumpkins), Phytophthora blight. Both anthracnose and Phytophthora blight usually cause lesions on the bottom of the fruit. Such lesions result from spores that splash from leaves. It is difficult if not impossible to coat the bottom of the fruit with fungicide. Instead, the idea is to protect the foliage so fewer spores splash from foliage to fruit. Plectosporium blight and bacterial spot are unlikely to develop on fruit in the last few weeks before harvest.

Tomato/pepper-bacterial spot, bacterial speck and bacterial canker are the diseases most likely to affect the fruit (bacterial speck and canker are mostly tomato diseases). Bacterial canker is a systemic disease—the bacteria moves within the plant—thus, it is unlikely that an application of a bactericide within days of harvest will make any difference in control. Bacterial speck is mainly an early season disease and is not as common as bacterial spot. Applications to control bacterial spot will probably not be effective within 7-10 days of the final harvest. Remember, that bacterial spot and speck are very unlikely to occur in a greenhouse situation.

Broccoli/cabbage-Alternaria leaf spot may directly affect broccoli heads. Therefore, applications within 7-10 days of the final harvest are probably warranted if the disease has been observed.  Alternaria leaf spot and black rot may affect cabbage heads directly. However, late season black rot or Alternaria leaf spot on outer cabbage leaves will probably not affect marketability.

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