There has been a number of reports of a strange tissue growth on the stems of compound leaves and even around developing nutlet. There are three species of phylloxera on pecan. Most everyone is familiar with the species that causes warts on the leaves referred to as Leaf Phylloxera. Tiny, soft-body, aphid like insects feed on developing leaf tissue in the spring in which a gall or wart forms which protects the insects. If you take a knife and cut open the wart, you will see the insects inside. They overwinter in the crevices of the bark before they feed on green tissue at budbreak. Leaf phylloxera is not much of an economic pest as long as you treat the following year to control them. Stem phylloxera is a bit different, however.
2023 was the first I observed stem phylloxera. Last year, some older ‘Stuart’ and ‘Schley’ were shedding leaves in early June with the concern that leaf shed be from stem phylloxera. It has been noticed when stem phylloxera was observed, pecans may shed leaves. This is why this species is more of a concern.
This year, the calls of stem phylloxera have come from Northeast Georgia and in older, less managed, sometimes backyard orchards. I did visit one of these sites which is a commercial orchard. Stem phylloxera had never been observed in this particular orchard. We were able to locate stem phylloxera on most trees; however, it was only 15 % of trees that were severely infested. On those infested trees, every single terminal had stem phylloxera. So far, Morgan County is the furthest south I’ve heard reports. The furthest north is Lincoln County.
Control
As with leaf phylloxera, treatment will have to occur in the spring of 2025. Once the galls form, the insecticide cannot penetrate the gall to kill the phylloxera. Imidacloprid is effective at controlling phylloxera, but the timing is critical. The application must be made at budbreak, once green tissue has emerged. You may need to treat twice if the timing of budbreak is different among varieties.
Written by: Andrew Sawyer, Southeast GA Area Pecan Agent & Dr. Apurba Barman, Entomologist
