Severe Drought Management
Recommendations For Almonds
By David Doll, UCCE Farm
Advisor, Merced County
UC researchers have urged growers not to take aggressive actions in
reducing tree size or crop load in response to the West side water shortages
this year. Severe pruning will increase new growth which would increase the
leaf surface and evapo-transpiration rates (ETc) of the tree. Crop thinning has
a similar effect and is also not recommended.
|David Doll, UC Farm Advisor, Merced.|
By reducing crop load, the source/sink ratio of the tree is disturbed,
causing the tree to put nutrients into vegetative growth instead of the nuts.
Furthermore, data suggests that less than 10% of ET may be attributed to crop
load. The tree should thin naturally when it undergoes a late-spring water
stress period. Furthermore, in season nitrogen applications should also be
reduced in order to reduce vigorous shoot growth.
In scheduling irrigation, the pressure chamber should be used to determine
the stem water potential of the trees. Orchard irrigations should not be
initiated until the trees reach -15 bars. Irrigations should be at the
percentage of ET that can be afforded – for example: if 15% of water available
for the season, water at 15% ET at each irrigation. Research by David Goldhamer
suggests that almond trees can survive through the year on as little as 6-8
inches of water (5- 10% ET). This includes the 2-4 inches of water available
within the soil profile.
Further reduction of inputs this coming year is advised for the growers
facing water restrictions. Reductions of in-season fertilizers and foliar
nutrients will help decrease the vigor of the tree. Use judgment in making
these cutbacks as the goal is to reduce tree vigor, not to make the trees deficient.
Post harvest fertilizer applications are still recommended. Furthermore, it is
not advised to cut back on miticides. With severely stressed trees, mites can
flare up easily, causing defoliation and adding to tree stress.
If the orchard has a history of pyrethroid use, miticides will most likely
be necessary for the coming growing season. If softer chemistries have been
used, sprays may be limited or unnecessary. In these cases, monitoring the
population of mites and beneficials will be needed throughout the season to see
if they approach the treatment threshold.
A light pruning or topping, may be a feasible practice to stop new shoot
growth in the spring. Once the trees push new growth, heading cuts would
terminate shoot growth, thus reducing leaf surface area. This may work if
nitrogen rates were reduced – otherwise the tree would push again causing more
tree stress. There is no direct data that supports this practice, and it may
not be worth the effort or expense.
In general, if the tree is able to maintain some of its leaves until the
fall, the tree probably will survive. Yields will be affected severely for the
next 2 years. This year would be a good year to remove older blocks with
declining production and divert the water to younger blocks if possible.
Labels: Almond Drought Management.By David Doll, Merced County, UCCE Farm Advisor