Commercial Disease Controls
The Pennsylvania State University
Cooperative Extension

Summer Squash

Seed Treatment

Check with seedsman to determine if seed has been treated with an insecticide and fungicide. If it has not been treated, use a mixture of thiram 75WP (1/2 teaspoon per pound or 3 ounces per 100 pounds) and an approved commercially available insecticide.

Disease Control

Damping-Off
Apply the following in a 7-inch band after seeding. Use formula in the "Calibration for Changing from Broadcast to Band Application" section of Calibrating Granular Application Equipment to determine amount of Ridomil Gold or Ultra Flourish needed per acre.

mefenoxam -- 1-2 pt Ridomil Gold 4E/A or 2-4 pt Ultra Flourish 2E/A

Viruses (CMV, WMV, PRSV, and ZYMV)
Resistance to many viruses is available; use resistant varieties. Varieties expressing the precocious yellowing gene such as Multipik mask the greening caused by WMV and CMV but will become distorted when infected with either PRSV or ZYMV. PRSV is devastating in some squash fields in the region and, where this virus is present, resistance to all viruses is necessary. The following control measures should also be used.

Plant fields as far as possible from existing cucurbit plantings to prevent aphid transmission of viruses from existing fields to new fields. Also, use reflective mulch to prevent aphid transmission of viruses.

Bacterial Wilt
Insect control is essential for prevention of wilt. Control cucumber beetles before they feed on plants.

Powdery Mildew
The fungus that causes powdery mildew has developed resistance to several classes of fungicides. The fungicides at risk for resistance development such as Strains of the pathogen that are highly resistant to some strobilurins/Class 11/QoI fungicides (Cabrio, Flint, Amistar, Quadris and Tanos) have been reported in the Eastern U.S. in 2004 and 2005.

Powdery Mildew generally occurs from mid-July until the end of the season. Excellent resistance is available in all recommended cucumber varieties. Observe fields for the presence of powdery mildew. If one lesion is found on the underside of 45 old leaves, begin the following fungicide program:

Alternate:
Chlorothalonil (Bravo, Echo, Equus)--2-3pt 6F/A or OLF plus Nova--5oz 40W/A, or
Chlorothalonil (Bravo, Echo, Equus)--2-3pt 6F/A or OLF plus Procure--4-8 oz 50WS/A,

with a tank mix containing chlorothalonil and

Pristine--12.5-18.5 oz 38WG/A

Downy Mildew
The disease generally does not occur until mid-August, however, scout fields for disease incidence. Refer to the Cucurbit Downy Mildew Forecasting website (http://www.ces.ncsu.edu/depts/pp/cucurbit/) for current status of the disease. Begin sprays when vines run, or if disease occurrence is predicted for the region. Preventative applications are much more effective than applications made after disease is detected. Resistance to the QoI/Class II fungicides has been reported in the Eastern U.S. The following are the most effective materials (tank mix these products with a protectant such as chlorothalonil (Bravo, Echo, Equus)--1.5 pt 6F/A or OLF or maneb--2-3 pt 4F/A or OLF):

Ranman--2.1-2.75 fl oz 400SC/A or
Previcur Flex--1.2pt 6F/A or
Curzate--3.2 oz 60DF/A or
Pristine--12.5-18.5 oz 38WG/A, or
Tanos--8 oz 50 WDG/A or
Cabrio--8-12 oz. 20WG/A.

Materials with different modes of action (FRAC group) should be alternated.

Sprays should be applied on a 7-day schedule. Cabrio, Pristine and Tanos should not be alternated with each other or used consecutively. Under severe disease conditions spray interval may be reduced if label allows.

Plectosporium Blight (Microdochium)
Rotate with crops other than cucurbits. It is important to achieve maximum foliage coverage with the fungicide application. Once symptoms appear on petioles or after fruit form, apply the following and repeat every 7 - 10 days:

chlorothalonil (Bravo, Echo, Equus)--1.5-2 pt 6F/A or OLF mancozeb (Dithane, Manex II, Manzate, Penncozeb)--2 lb 75DF/A, or
maneb--2-3 pt 4F/A or OLF)

A spray schedule that alternates Cabrio or Flint with chlorothalonil will also provide control.

Blossom Blight
This is a serious problem in some years. The fungus becomes established in senescent blossoms and grows into young fruit. Improve aeration through wider plant spacing and good weed control.

Scab
Disease occurs during cool periods. Use resistant varieties when possible. Begin sprays as true leaves form. Repeat every 5 to 7 days.

chlorothalonil (Bravo, Echo, Equus) -- 2-3 pt 6F/A or OLF

Phytophthora Blight
To minimize the occurrence of this disease, squash should be grown on raised beds, and field should be adequately drained to ensure that soil water does not accumulate around the base of the plants. Mefenoxam (Ridomil Gold or Ultra Flourish) should be applied preplant for early season control. Once the canopy closes, subsoil between the rows to allow for faster drainage following rainfall. When conditions favor disease development, apply the following:

Forum--6 oz 4.18SC/A (must be tank-mixed with another fungicide active against Phytophthora blight on summer squash such as fixed copper), or
Gavel 1.5-2 lb 75DF/A, or
Tanos--8 oz 50 WDG/A (suppression only), or
Ranman--2.75 fl oz 400SC/A

Note: Where trade names are used, no discrimination is intended and no endorsement by the Cooperative Extension Service is implied. Information provided is intended for consideration by the user, but is not intended to be a recommendation. Production decisions should be based on consideration of many types of information (scientific, experiential, economic, legal, etc.) available to the user.