Gordon Johnson, Extension Vegetable & Fruit Specialist; gcjohn@udel.edu
Over the last 2 weeks we have had freezing temperatures in some locations, high winds, and wind-blown sand that have damaged early planted vegetables. May 7 and 8 saw sustained high winds with peak gusts over 30 mph causing significant plant stress and injury.
This combination has resulted in extensive damage in vegetable crops. Some symptoms are marginal leaf burn, leaf bleaching, leaf desiccation, leaf dropping, stem browning, and in some cases, plant losses. Symptoms are most severe on newly transplanted crops or transplants that have not yet rooted in well. In conventionally tilled field there was extensive sandblasting on our light soils with high winds.
Growers with damage should evaluate plants for the extent of damage and need for replanting. Wilted, snapped, broken, or severely “wind burnt” plants may need to be replaced. Growers should also consider applying protectant fungicides/bactericides to reduce infections by opportunistic disease organisms on damaged tissues.
Potatoes
Damage on potato will appear 1-3 days after the freeze event. The symptoms commonly will be black areas on leaves that dry out. Seed pieces are well below ground and will not be damaged. If the apical meristem is killed, the growing point will move to an axilliary bud(s) lower on the stem and growth will continue. The plants may be set back a few days depending on the severity of the damage. Temperatures between 29-32 °F will cause minor injury, but temperatures below 28 °F may kill the plant to the ground.
Cantaloupe
Early planted cantaloupe has been damaged by cold temperatures and high winds. Symptoms of damage are desiccation, dry paper like leaves, light brown to tan areas on leaves, stem browning and plant wilting. Cantaloupes with cold damage will likely remain stunted and may need to be replanted.
Watermelons
Several hundred acres of watermelons were transplanted over the last 2 weeks on Delmarva. Freezing temperatures and high wind caused severe damage in some fields that will require selective replanting. Fields with strong rye windbreaks had the least damage. Wind-blown sand has “sandblasted” some fields. Symptoms of damage on watermelon will be dark brown to black areas on leaves that become papery. Plants with live growing points will recover; however, If the growing point was damaged, the plants would have to regrow from the buds at the cotyledon.
Sweet Corn
Hundreds of acres of both processing and fresh market sweet corn have been planted. Growth has been slow and many fields have freeze and “sand blasting” damage. Effects on corn will depend on where the growing point is and if the growing point was damaged. At V-4, the growing point is just below the ground. By V-6, the growing point is above the ground. For most sweet corn, a light freeze will damage the leaves but the plants will continue to grow because the growing point is still alive. In a sand-blasted field, even though the growing point is still below the ground, the plant is cut off at the soil line. There are no leaves left and an open wound subject to disease entry. These fields may have to be replanted.
Peas in Flower
Peas in flower can tolerated short periods below 32 °F (a few hours). However, several days in a row with night freezes will cause yield losses. The most common symptom of damage to peas is blanks where seeds are missing in the pod due to incomplete pollination. This has been observed in early varieties such as Jumpstart in the past.
Tomatoes
Throughout Delaware, freezing temperatures damaged or killed unprotected tomatoes. Tomatoes are a warm season vegetable that cannot tolerate any frost or freeze event. Damaged plants will have to be replaced.