I have been in a few orchards this past week and thought I would relay on some thoughts.
1). Bloom. In comparison to last year, bloom seemed to last much longer. Some orchards I have been working next to are now entering petal fall. Their first blossoms opened up about 20 days ago. It appears that the trees hit full bloom in our area during the nice weather that we had last week. Hopefully this will aid in pollination and nut set.
2). Frost Damage. Frost damage appeared to be pretty minimal (1-5%) in the 15 or so orchards I checked around Merced County. I have heard mumblings that damaged pistils and stamen from the extreme temperature may lead to poor pollination and nut set. At this time, it is hard to predict if this occurred and to what extent. Most likely this type of damage will become apparent during the flower drop and nut drop periods. Keep in mind that other weather issues may contribute to these drops making it hard to determine what caused what.
3). Fungicide Sprays. The threat of Brown Rot is still pretty high, especially with Butte/Padre orchards. This weekend we saw great weather for Brown Rot – over 60F and raining. The winds today have aided in the reduction of leaf wetness, thus reducing brown rot risk. If Sat/Sun/Monday’s rain event fell in the 10 day window from your last spray, it looks like you may be able to get through this week without too much worry – unless the weather changes! You have at least 10-12 days of protection after a fungicide spray.
As petal fall approaches and we move into leaf out and nutlet formation, keep an eye out for shot-hole, jacket rot, anthracnose, and scab. Of these four diseases, scab requires the latest treatment – 2-5 weeks post petal fall. If you have had a history with scab, try to hit on the earlier side of this window – even if that means spraying again for rust!
I was in a few orchards today that experienced late season defoliation due to scab. Needless to say, their bloom density was lower than expected.
4). Fungicide rotation. Fungicide rotation is critical to maintaining the life of a fungicide mode of action. Keep in mind that some fungicides may have the same type of active ingredient. A good example is Gem and Abound – different trade names, but the same basic chemistry. Follow the FRAC numbers to help avoid confusion due to trade names – do not use fungicides with the same FRAC number in back-to-back applications.
5). Nitrogen Applications. In areas of high rainfall and coarse soil, it is a little on the early side to be applying nitrogen. Wait to apply nitrogen until the leaves are expanded and actively transpiring. The tree will not “sniff out” and absorb nutrients within the soil; it requires the process of osmosis and diffusion to move the nutrient-water solution into the plant in order to maintain the water gradient (wettest to driest).
Leaching of nutrients, especially in coarse soils, can occur easily. Excessive rainfall can move applied fertilizers below the rootzone, wasting money and adding to the groundwater contamination problems.
You may have heard that growers in the southern San Joaquin Valley are applying some nitrogen now. For the most part, they are able to get away with this because their annual rainfall rarely exceeds the water holding capacity of their soils, thus reducing the risk of leaching the nutrients out of the rooting profile.