Jerry Brust, IPM Vegetable Specialist, University of Maryland; jbrust@umd.edu
I have been seeing and receiving a few samples of yellowing (chlorosis) around the margins of cantaloupe leaves (Fig. 1). There was no chlorosis between the veins and no marginal necrosis (these two symptoms would indicate molybdenum deficiency). The marginal chlorosis 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. Water droplets from the plant accumulate at the edge of a leaf in the early morning. This water often contains organic and inorganic compounds, and mineral nutrients, especially potassium. As the water evaporates these compounds are left behind and concentrated at the leaf margin. Over time the high concentration of compounds shows up as a marginal yellowing called ‘salt burn’. These deposits also can have a toxic effect on the gas exchange pores (the hydathodes) located at the leaf edges. Salt accumulation often is associated with foliar applications of nutrient solutions or pesticides during very hot, dry weather. Frequent copper applications when it is hot and dry also can result in distinct bands of yellow tissue around leaf margins (Fig. 2). Soil applied urea or ammonium nitrate fertilizers may contribute to the problem as well. In most cases there is no yield loss as a result of these symptoms and no control measures are needed; however there could be yield losses if salt burn is severe and widespread in the field.
Figure 1. Marginal chlorosis on cantaloupe leaves (arrows) caused by salt burn
Figure 2. Marginal chlorosis most likely caused by copper sprays and salt burn