Cucurbits

Starting to see some watermelon, cucumber and other cucurbit crops that are looking a bit pale green or even yellow (fig. 1). Sometimes the plants have brown speckles or spots on them that may look like a foliar disease has started (fig. 2).

This heat wave we have had this past week will have repercussions over the next few weeks as the flowers of several crops including cucurbits, peppers and especially tomato will not pollinate or fertilize properly to develop into fruit. Daytime highs of 90o F and above and nighttime lows only getting down to 70o F in much of the midAtlantic for the last week will cause blossom drop and fruit abortion in tomatoes.

I have been seeing some ozone damage to cucurbits and oddly to tomatoes over the last 2 weeks or so, which is not unusual with the hot hazy conditions we are having. Ozone is the most common air pollutant in the eastern United States.

The weather for the last week or so in our area has been ideal for air pollutants to cause injury to vegetable crops, especially cucurbits. One of these air pollutants is ozone, which is considered to be the most damaging phytotoxic air pollutant in North America. Injury is most likely during hot, humid weather with stagnant air masses.

I am seeing some plectosporium blight in a few pumpkin fields this year, not as bad as last year but still there. This disease will probably increase if we continue having frequent rains in some locations.

One of the main things a grower can do to ensure a good quality pumpkin is to be sure they maintain their fungicide applications for as long as they continue to harvest fruit. Maintaining good foliage cover for your pumpkins results in pumpkin handles that are dark green stout and firm (fig. 1).

I have been seeing and receiving a few samples of yellowing (chlorosis) around the margins of cantaloupe leaves (Fig. 1). The marginal chlorosis observed in figure one would indicate salt burn, which is a noninfectious problem that mostly affects cantaloupes. This yellowing at the leaf margin is likely the result of guttation, which is how plants exude water at the margin of the leaf.

There have been several reports of odd looking damage to watermelon transplants being grown in greenhouses these past couple of weeks. The damage does not appear to be cold damage per se, but more of a strange environmental/weather one. Watermelon transplants, along with some other vegetables, began showing dark pitted lesions on their cotyledons (fig. 1).