Fruit trees are interesting plants to grow. Humans have been selecting for better fruit for centuries, and in the process, some of the natural resistance to pests and diseases have been lost. A further challenge is our mild rainy climate, which is perfect for fungal and bacterial diseases that affect fruit trees.
Customers often ask me, ‘when should I do a dormant spray?’ Old school was to spray oil while your fruit trees were fully dormant. Today, we’ve found that it is more effective to spray oil combined with a bactericide or fungicide at specific stages of bud development, also called bud stages. By using bud stages to time our sprays, we end up spraying less- always a goal in the orchard.
In February, we posted about timing sprays for Peach Leaf Curl. Recently, plum and cherry buds are starting to swell, so now’s the time to look at your trees for timing. Stage 3 flower buds is a perfect time to spray an oil plus copper for cherries and plums. What do these sprays do?
- Oil in delayed dormant sprays smothers overwintering aphid and mite eggs
- Copper helps prevent bacterial canker infections, blossom blight and brown rot in stone fruit trees.
Some years, our stone fruit trees can be at stage 3 (just before bloom) in February. This year the bloom has been delayed by the extended cold weather we had January through early March.
How about your apples and pears? We’re not quite there yet on those, but here are the signs you should be looking for: apples and pears should get a spray of oil plus sulfur between stages 4 and 6.
- Again, the oil in the delayed dormant spray will smother overwintering aphid, scale and mite eggs
- Sulfur helps prevent powdery mildew at this stage.
Once pears and apples hit stage 4, the flowers can open pretty fast. If you grow varieties that are susceptible to apple or pear scab, you will need to be ready to spray a sulfur spray (with no oil) once your blossoms swell just to the point of showing color (pre-pink, or stage 6). Add Bacillius thurengenisis (Bt) to this spray to get the first hatch of leaf rollers. A second sulfur spray at petal fall will keep your trees healthy and mostly scab free.