Gummosis is often apparent near harvest on the surface of peach fruit, especially in organically grown or minimally sprayed orchards. Gummosis appears as beads or a string of clear ooze after certain types of plant bugs (Nezara virdula, Acrosternum hilare, Halyomorpha halys) puncture the skin of the peach to feed (Figure 1). This year stink bugs have caused much of the gummosis observed at harvest in central Missouri. Dry, corky, sunken areas also occur just beneath the feeding site in the fruit flesh. Gummosis can be brushed off the fruit and the superficial damage in the flesh can be cut out. While stink bug feeding results in slight imperfections in the appearance of the peach, the fruit is safe to eat.
Gummosis can also occur on developing peach fruitlets in the spring as a result of tarnished plant bug (Lygus lineolaris) or stink bug feeding. When peaches are about ½ to ¾ inch in diameter, feeding by either type of plant bug causes not only gumming of the fruit, but also severe catfacing damage, fruit distortion, or fruit drop. Tarnished plant bugs are attracted to orchards where winter annuals are in bloom. Controlling broadleaved winter annual weeds and legumes, such as clover and vetch, in and surrounding orchards can reduce the incidence of plant bugs. Because these plant bugs are in orchards in early spring before peach trees bloom, scouting for these insects is recommended at the pink floral bud stage (before any flowers are open). Insecticide may be applied at the pink stage when tarnished plant bugs or stink bugs are found. Stink bugs feed throughout the growing season and may have one or two generations per year, depending on the species. Tarnished plant bugs have multiple generations each year. Thus, these insects require monitoring until harvest even though they may begin to leave peach trees for other hosts after petal fall.
Yet another insect that causes gummosis on peach fruit is the Oriental fruit moth. However, unlike the plant bugs, gummosis resulting from Oriental fruit moth feeding contains frass (excrement from larvae). In the spring, a larva bores into a terminal shoot, causing it to wilt. Later, a larva may bore into the peach fruit near the stem and burrow through the fruit. When it exits the peach, a hole with gumming and frass remains on the surface of the fruit. Monitoring for Oriental fruit moth also begins at the pink stage of flower development and continues through October since there are multiple generations of these insects during the growing season. Homeowner recommendations for controlling insect pests may be found at: extension.missouri.edu/publications/DisplayPrinterFriendlyPub.aspx?P=G6010 and those for commercial orchards are at: https://ag.purdue.edu/hla/Hort/Pages/sfg_sprayguide.aspx.
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REVISED: February 21, 2017