Wall-O-Water Tomatoes With Yellow Spots on the Leaves

Low Temperatures

• The water in each chamber of a Wall-O-Water holds heat from the sun, helping warm the air around plants during cool nights. A Wall-O-Water protects plants to just below 20 degrees Fahrenheit. As the water freezes, heat is released, warming the air around the plants; however, once the water is frozen, the heat source is exhausted, so the device won’t protect against extended periods of low temperatures.
  Tomatoes are warm season crops and do not like cool temperatures. Such conditions can lead to slow growth and pale leaves, which are a sign of stress, according to the Colorado State University Cooperative Extension.

Cold Damage

• The construction of Wall-O-Water devices allows them to be left open or closed. If you notice yellow spots on your tomato plants' leaves and you use the device around mature plants, the spots may be the result of cold damage. Portions of your tomato plants that extend above and outside the device do not receive protection from frost or low temperatures. Such damage may lead to discoloration, yellowing, withering and water-soaked spots on foliage.

Moisture

• The accumulation of moisture inside the device can create conditions favorable for fungal disease to develop. Leaf mold, caused by the fungus Fulvia fulva, leads to yellow spots on the tops of tomato foliage, spore masses on undersides of leaves and leaf drop.

  Poor air circulation is a major factor in development of the disease. Plants surrounded by a Wall-O-Water device may be more susceptible because they receive less exposure to wind that can help dry their foliage. Removing the device will help reduce humidity around your plants. Water plants at ground level, and monitor plants inside the device for signs of disease. Fungicide treatments are available.

High Temperature, High Humidity

• Wall-O-Water devices collect solar heat to increase the temperature of the soil around your plants, as well as the air. This may give tomatoes planted early in the season a boost in growth, but you risk creating conditions of high temperature and high humidity around your plants which can lead to early blight.

  If you are using a Wall-O-Water to prevent damage from late spring frosts, monitor your plants for the target-shaped spots surrounded by yellowed tissue that mark the infection. Consider removing the device if high temperature and high humidity conditions develop. This may happen if you leave the device on during day in warmer weather. Fungicide treatments, including fixed copper, are available to treat early blight.