2016 Mid-Spring Update

The crop is developing nicely in many areas across the areas of the San Joaquin Valley in which I observed. Crop loads vary, depending on last season's stress or crop-load, but generally look good. Looking forward to this week, there area few pointers to keep in mind.

1. Rain is forecasted for this weekend with chances through next week. This will have minimal impacts on the physiological development of the crop. It will, however, impact the amount rates of evapotranspiration and soil moisture. This variance should be accounted for by either using soil moisture monitors or plant based measurements. If possible, rain gauges (or other measurement tool) should be placed at the various farms as rainfalls can be variable. Last year, for example, a thunder cell dropped around 3/4" of rain in a farmer's field on the North side of Livingston, while his block on the south side received less than 1/4." Accounting for these differences can prevent the "stalling-out" of growth from over-irrigation.
2. Even though it warmed up this week, it might be wise to question the start of the irrigation season. Only two out of four plots in which we are measuring stem water potential have indicated the need to irrigate. The other two are still reading around baseline...one is even in a Delhi sand. Plant based measurements should be used to help determine the need to irrigate. Remember: the tree is essentially a giant tensiometer with a lot larger volume of soil impacting the result.
3. Disease update: Multiple days of rain are predicted. This could mean conditions suitable for Bacterial Spot (especially on 'Fritz' and 'Padre'), Anthracnose (for 'Monterey'), Scab, and Shot-hole. Lingering infections of green fruit rot may also progress. If a treatment is warranted, check the fungicide efficacy table. Remember to rotate away from the last spray that was applied. Also, with the exception of manzate and copper, fungicides are not effective on bacterial spot.
4. Fertilization rates should be matched to expected crop yields. It is never easy to estimate crop, but being close is good enough as there is time to adjust fertilizer rates during the post-harvest period. Remember, for every 1000 kernel pounds/acre of expected crop, 95 pounds of N need to be applied. UC Research in Kern County did not find a yield benefit (short or long term) from applying more than 250 lbs of N/acre. More information can be found here.
5. Depending on soil type, in-season potassium fertilization may also be needed. Soils with low CECs (<12 meq/100 g) should consider in-season potassium applications through the irrigation system. There are a number of products to consider, all with their own pros/cons. These include potassium nitrate, potassium thiosulfate, potassium sulfate, potassium chloride, potassium carbonate, and probably a few more. Many liquid blended fertilizers containing K often contain it as either potassium thiosulfate or potassium chloride. Heavier soils with high vermiculite content might be able to help increase the availability of K with acidifying agents, especially in alkaline soils.
6. Pre-emergent herbicides. We have been getting an increase in the number of pre-emergent herbicide uptake occurrences. So far, these have been linked to mis-applications due to the applicator error (Not paying attention, poor nozzles/application uniformity, dismounting the rig without shutting it down, slowing at the end of the row, etc). This over-application mixed with feeder roots closer to the surface of the wetting profile due to the drought is the current thought on why these cases are occurring. Be careful with your herbicides - and do what is possible to avoid drift during the windy days of spring.