Rain is predicted for later this coming week (Sat through early the following week). This looks to be a multiple day storm with rain potentially falling for 3-4 days. Temperatures will be between 40-60F. These conditions are favorable for a number of post bloom/petal fall diseases, including brown rot, shot-hole, jacket rot (or green fruit rot), anthracnose, and bacterial spot.
The almond fungicide efficacy table should be consulted to help with fungicide selection. An updated 2015 Fungicides, Bactericides, and Biologicals for Deciduous Tree Fruit, Nut, Strawberry, and Vine Crops can be found here. Scroll to page 31 to find the efficacy of many common fungicides. Please not that not all fungicides are listed due to the inability to test all trade names. If a fungicide isn’t listed, check to see if the active ingredient is provided, and if not, check the efficacy of the FRAC group. The table on page 32 provides treatment timings which indicate susceptibility of almond to diseases at various growth stages. Finally, page 33 highlights various fungicides that are effective on diseases at specific growth stages and can be used to help determine a rotation.
A fungicide product should provide coverage for the above diseases. Products used in earlier fungicide sprays should be rotated to another mode of action (or FRAC group). This should still be considered even if the FRAC number was one part of a combination product. Rotation helps to preserve fungicide efficacy, which leads to a longer product life (and eventually cheaper prices).
Some interesting points to keep in mind when reviewing the tables:
- FRAC 3 fungicides are not very effective on jacket/green fruit rot;
- Bacterial spot control will require the use of copper, Manzate Pro-Stick, or combinations of the two products. Keep in mind that almond trees are sensitive to copper. More info on this disease can be found here;
- If the wet pattern continues, a broad spectrum material may be needed to rotate away from the commonly used FRAC 3 and FRAC 11 groups. In these cases, consider chlorothalonil, Captan, Ziram (or Manzate Pro-Stick), or other broad spectrum fungicides;
- Fungicides will maintain activity for about 2 weeks with no rainfall, and about 7-10 days with consistent rain. If a wet pattern occurs, several spray may be needed to provide disease control.