- Author: Ben Faber
Drought may not be the right time to be thinking about this, or maybe it is. It concerns managing water and any time a grower uses water more effectively the crop performs better. But fog can be a significant factor in water management.
As fog passes through a tree canopy, it is absorbed by leaves and coats them. Before the tree will transpire water, the water coating must first be evaporated before the tree loses internal water. This water use is not accounted for in a water budget schedule using evapotranspiration based inputs, such as from CIMIS. For deciduous trees, this is often not of concern, because in the winter they don't have leaves and therefore are not transpiring anyway. For evergreen subtropicals like citrus and avocado, this could be an important source of water.
In many situations in the Central Valley and along the coast there can be periods where fog can represent a significant proportion of the water requirement for an orchard. These periods would be for winter tule fog in the Valley and along the coast in the spring and early summer. A recent publication by Rick Snyder at UC Davis has just been released that shows how this fog water can be incorporated into an irrigation schedule. You can see it at the UC's California Institute for Water Resources website: http://anrcatalog.ucanr.edu/pdf/8532.pdf, http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
- Author: Ben Faber
When reviewing possible problems your citrus might have, it's easy to jump to the conclusion that it is a virus. That's because viruses are a major problem around the world in citrus and the effects can be slow, chronic and debilitating or fast and deadly. Images get posted on the web, and if those symptoms look like something your tree has, then by golly you have a virus. Well, actually viruses are everywhere and in most plants, so you probably do have a virus or viruses, but not plant debilitating one. California, has had a pretty thorough nursery inspection procedure in place for many years and the likelihood of a virus causing a problem is less likely here than in many parts of the world.
In most cases viruses are difficult to eradicate in practice, so it is best to remove them before they get out in the field. The Citrus Clonal Protection Program (http://www.ccnb.info/page.php?s=2&c=3) weeds out citrus viruses before they get to wholesale nurseries and into the trade. That does not mean that we don‘t have debilitating viruses in the California industry. We do. Tristeza is in some of our orange orchards and that can lead to significant yield reductions and tree death (http://www.ipm.ucdavis.edu/PMG/r107101311.html.). Tristeza is spread by the melon aphid and is hard to control without good control of the aphid. In many older orchards there is exocortis and psorosis http://www.ipm.ucdavis.edu/PMG/r107100100.html; http://www.ipm.ucdavis.edu/PMG/r107100511.html). These are graft transmissible and why it is not good, in fact unlawful, to propagate trees with uncertified budwood.
In most cases in California if you are having symptoms of unhealthy in your trees it's most likely due to an irrigation problem (too much, too little, poor timing), a nutrient deficiency and possibly a fungal disease (most likely a root one such as armillaria or Phytophthora). Or in this day, it could be the start of Huanglongbing vectored by Asian Citrus Psyllid (http://www.ipm.ucdavis.edu/PMG/r107304411.html). Before jumping to the conclusion that there is a virus in your trees. Check out the most common problems for California citrus first (http://www.ipm.ucdavis.edu/PMG/C107/m107bpleaftwigdis.html). There are enough of those anyway.
Boron toxicity
- Author: Ben Faber
Transpiration is essentially a function of the amount of leaves present. With no leaves, there is no transpiration and no water use. The extreme case is tree removal. If canopies are pruned there is reduced water use. The more canopy reduction, the more transpiration reduction. Most citrus produces terminal flowers, so there is also a reduction in yield, but there is also typically an increase in fruit size as competitive fruit growing points are removed. There is a balance between yield reduction and tree water use, but typically a 25% canopy reduction results in a 25% decrease in tree water use (Romero, 2006).
The severity of the drought will determine how drastic the canopy should be trimmed. The trees can be skeletonized so that only the main structural branches are left. The tree is whitewashed to prevent sunburn and the water is turned off. As the tree gradually leafs out, the water is gradually reapplied in small amounts. It's important to check soil moisture to make sure the tree do not get too much or too little water. The trees if pruned in the winter will often flower a year later in the spring, but normal production will often take three years for the trees to recover their previous yields.
Skeletonizing should first be practiced on orchards that are the poorest producing. In those areas that get too much wind and have lots of wind scarring or elevated water use, those areas that are most prone to frost damage, those areas that have been always problematic, such as fruit theft. In areas that are healthy and a new variety has been contemplated, this is the time to topwork and replace that old variety. In areas that have been poor producing from disease, this is the time to get rid of those trees.
Canopy sprays of kaolinite clay have shown some promise in reducing transpiration with negligible yield reduction (Skewes, 2013; Wright, 2000). If these are used, they should be done under the advisement of the packing house to make sure the clay can be removed in the packing house.
With a reduced canopy, there are often other benefits besides water reduction. There is better spray coverage for pest control. There is also reduced fertilizer use. New growth is normally coming from nutrients that are now being mined by a large root system and fertilizer applications can be significantly reduced or eliminated altogether for a year until fruit set recommences.
Citations
Kerns, D. and G. Wright. 2000. Protective and Yield Enhancement qualities of yield of kaolin on lemon. In: Eds. G. Wright and D. Kilby, AZ1178: "2000 Citrus and Deciduous Fruit and Nut Research Report," College of Agriculture and Life Sciences, University of Arizona. http://extension.arizona.edu/sites/extension.arizona.edu/files/pubs/az1178_3.pdf
Skewes, M. 2013 Citrus Drought Survival and Recovery Trial. HAL Project Number CT08014 (16/12/2013). SARDI. http://pir.sa.gov.au/__data/assets/pdf_file/0004/238414/SARDI-Citrus-Drought-Survival-Recovery-Trial.pdf
Navel trees skelotinized and topworked, ready for rain and more profits in the future.
- Author: Ben Faber
Water moves in a wetting front. When irrigation water hits the soil it moves down with the pull of gravity and to the side according to the pull of soil particles (more lateral with more clay). Soil is a jumble of different sized soil particles, from clay to silt to sand sizes and then often intermixed with stones of different sizes from gravels to boulder. The different textures determine how water moves. It moves fastest through coarse textures and slowest through finer ones – the clays, the ones with the smallest pores. But soils are a jumble of particle sizes and pores.
Water first moves down the larger pores and then it slowly moves through the larger ones. As water moves through the soil it carries salts that have accumulated in the soil. At the wetting front is where the salt accumulate. As the water moves through the larger pores, salts migrate/diffuse from the small pores to the larger ones. This diffusion takes a bit of time, so typically the small pores have a larger salt concentration than the larger ones.
So an initial application of water will carry the salts from these large pores and if the irrigator were to stop in mid-application, it allows time for the salts to move out of the small pores into the larger ones. Then when the irrigation recommences, it will carry more of the salts out of the wetted area – the root zone. This technique is called “bumping” where an irrigation is stopped and then restarted in order to improve not only leaching, but also reduce runoff.
This principle also is at play when there are two or more sources of water quality. Soil salinity can be no lower than the irrigation water that is applied. Then as the soil water is removed through plant absorption or evaporation, the salinity increases. The soil salinity can easily be two to three times higher than the irrigation water.
If there are two sources of water, the initial application can be with the poorer quality water, and once that has reduced the soil salinity, then the better water quality can be applied which will then bring the soil salinity closer to that of the better quality water. By doing this two part leaching, the amount applied of the better quality water can be significantly reduced. This is a type of “bumping” to improve leaching.
Watch this U-Tube video on how water moves through soil, thanks to the work at Walla Walla Community College.
https://www.youtube.com/watch?feature=player_detailpage&v=J729VzBeI_g
Thank you Walla Walla Community College for the video
- Author: Ben Faber
Citrus response to irrigation water deficits have demonstrated that sensitivity of yield to water stress is dependent on the phenological phase in which water stress was applied. Adequate water supply is of major importance during citrus flowering and fruit set. A second critical period coincides with the period when fruit growth is rapid (fruit set to harvest). Depending on the level of water stress developed, the abscission of flowers and young fruits will be affected in the first case, as will fruit size in the second case.
For navels and mandarins it is possible to identify these critical periods in the crop and possibly allow stress when the trees are not in those critical periods. Some varieties though are complicated by having overlap of critical periods when another crop is present at the same time. Valencias can have two crops on the tree at the same time in spring and into summer harvest and coastal lemons can have fruit in all stages from fruit set to mature fruit at all times of the year. In the case of navels, reductions of applied water by 25% or more have resulted in no fruit yield reductions, if those water reductions do not occur during critical periods (Goldhamer, 2006; Domingo, 1996; Hutton et al, 2007). Water reductions during the rapid expansion period can result in significant fruit size reduction, though, and this period should be avoided if fruit size is critical to marketing (Goldhamer, 2006; Hutton et al, 2007).
In the case of coastal lemons, the stress should be avoided when the period of the most profitable crop is in rapid expansion, this is normally the summer crop. Each grower would need to identify, when the most profitable fruit size is important. Growers in areas that have more summer heat than the coast might practice a ‘Verdelli' irrigation practice, where water is withheld for a period of time, in order to force flowering that can often result in more summer fruit being harvested the following year (Maranto and Hake, 1985).
Citations
Domingo, R., Ruiz-Sanchez, M.C., Sanchez-Blanco, M. J. and Torrecillas. A.1996. Water Relations, growth and yield of ‘Fino' lemon trees under regulated deficit irrigation. Irrig. Sci.16: 115-123 http://link.springer.com/article/10.1007%2FBF02215619#page-1
Goldhamer, D. and N. O'Connell. 2006. Using Regulated Deficit Irrigation to Optimize Fruit Size in Late Harvest Navels. Citrus Research Board. http://citrusresearch.org/wp-content/uploads/2006-GOLDHAMER1.pdf
Hutton RJ, Landsberg JJ, Sutton BG. 2007. Timing irrigation to suit citrus phenology: a means of reducing water use without compromising fruit yield and quality. Australian Journal of Experimental Agriculture (47): 71–80. http://dx.doi.org/10.1071/EA05233
Maranto, J. and K. Hake. 1985. Verdelli summer lemons: a new option for California growers. California Agriculture 39(5): 4. https://ucanr.edu/repositoryfiles/ca3905p4-62870.pdf
Phenological stages of navel orange.