White Spots On Brambles

Gina Fernandez¹ and Herb Stiles²

¹Gina Fernandez, Ph.D.
Assistant Professor/Fruit Specialist
North Carolina State University
Vernon G. James Research and Extension Center
207 Research Station Rd.
Plymouth, NC 27962
Tel: 252-793-4428 ext. 167
Fax: 252-793-5142
Email:Gina_Fernandez@ncsu.edu

²Small Fruit Specialist
Southern Piedmont AREC
2375 Darvills Road
Blackstone, VA 23824
804-292-5331 Ext. 234
804-292-5623 Fax
rasbry@vt.edu

Spots on individual drupelets of both blackberries and raspberries may be caused by a couple of things. Stinkbug feeding on young fruits will result in a random pattern of white spots on mature fruits (photo 1). However, by the time that you notice the spots, the damage has been done by the stinkbugs and control is not possible for this year. When this type of damage on mature fruit is present the impulse is to spray the rest of the planting to prevent further damage. However, with flowers present you cannot spray insecticides because of bees. If you have damage this year, consider a pre bloom spray directed at the base of the canes next year. These stinkbugs overwinter in debris on the ground, and this spray will reduce the population.

A second cause of white spots is "sunburn" or "sunscald". Sunscald damage differs from stinkbug damage in that the shoulder or side of the fruit exposed to the sun will have a blanched or "cooked" appearance while the shaded side looks normal. There are differences in susceptibility of various cultivars to sunscald among available varieties, but none seem immune to there be no escaping it in this region. Damage can occur on both ripe and unripe berries (see photos 2 and 3). Damage usually occurs when the day begins with air temperatures near 90 F and that soon approaches or exceeds 100F. High relative humidity, still air and absence of cloudcover can aggravate the problem, but exposure of a hot drupelet to direct sunlight is the main problem. Under such conditions, we have observed sunlit drupelet temperatures that exceeded 115F. Average temperatures differed by more than 10 Fahrenheit degrees between the shaded sides and exposed sides of sunlit berries in one of our studies. Prolonged exposure to such temperatures can damage or destroy plant cells. The physical appearances of scalded drupelets seem to depend upon cultivar traits, stage of berry development; severity of injury, and time lapsed after infliction of the injury. Thus, drupelets may be white, pink, red, maroon, tan or brown, and they may or may not be shriveled and shrunken. The problem should not be present when cooler days arrive. Sunscald damage differs from stinkbug damage in that the shoulder or side of the fruit exposed to the sun will be white. Shift trellises can be used so that the plants own foliage provides shade to berries during morning hours. This keeps berries at or near air temperature during most of the day, so that occurrence of sunscald is greatly reduced