- Author: Ben A Faber
The USDA Pomological Watercolor Collection is one of the most unique collections in the Rare and Special Collections of the National Agricultural Library (NAL). As a historic botanical resource, it documents new fruit and nut varieties, and specimens introduced by USDA plant explorers from the late 19th and early 20th centuries.
The collection spans the years 1886 to 1942. The majority of the paintings were created between 1894 and 1916. The plant specimens represented by these artworks originated in 29 countries and 51 states and territories in the U.S. There are 7,497 watercolor paintings, 87 line drawings, and 79 wax models created by approximately 21 artists.
Lithographs of the watercolor paintings were created to illustrate USDA bulletins, yearbooks, and other publications distributed to growers and gardeners across America.
Today, the collection is preserved in NAL's Rare and Special Collections, where it serves as an important research tool for a variety of users, including horticulturists, historians, artists, and publishers. In 2010 and 2011, the entire printed collection was digitized to improve public access to this valuable resource, and to better preserve the paintings by reducing the need for researchers to handle them. Today, the whole collections is searchable.
In 1886, the United States Department of Agriculture (USDA) established the Division of Pomology to oversee the collection and distribution of new varieties of fruits, and to disseminate information to fruit growers and breeders. USDA commissioned artists to create technically accurate illustrations of newly introduced cultivars for the division's publications. In 1887, William H. Prestele was appointed as the first artist for the Division of Pomology. Henry E. Van Deman, division chief, explained the importance of Prestele's appointment in his 1887 Report of the Pomologist:
Up to August 1, when Mr. Prestele took his place here, there was no one to make drawings of fruits which were being daily received for study and comparison...but since then a part of the drawings have been made in India ink, and others have been reproduced in water-colors, all in the most skillful manner, showing the natural size, shape, and color of both exterior and interior of the fruit, with the leaves and twigs characteristic of each. These are invaluable for comparison and reference, and a portion for publication.
Over the years, other artists were also assigned to the division and their watercolors were used for lithographic reproductions in USDA publications and as scientific documentation of research results. Although some of the watercolor paintings are not signed, we know of 21 artists (nine of whom were women) who contributed to this important resource.
A more detailed history of the USDA fruit pictures is found in Paula Sewell's Garden History Girl blog:
Annona cherimola
- Author: Ben A Faber
UC Davis Ag Econ Department has put together a set of crop loss calculators in Excel. They are generic, but also specific to lemon and avocado. If you have had damage from the recent fire, take a look at them. At this point it may be too early to actually know the extent of the damage, but keep these in mind for the future.
Generic calculator: https://coststudies.ucdavis.edu/tree-and-vine-loss-calculators
Avocado: Avocado Trees, San Diego County (xls)
Lemon: Lemon Trees, Ventura County (xls)
- Author: Ben A Faber
The very fact that avocados can be grown in hard to get to places means that the trees are also in areas that are subject to wildfire damage. Recently several hundred acres of avocado burned in the Fillmore/Santa Paula foothills. The fire was fanned by high winds and low humidity. And in spite of being five weeks away from the June 1 weed abatement date, the green hills burned with fury.
Every year there are avocado trees that burn, either through careless attention to early morning fires that pickers build, wildfires or car accidents. A grower needs to be patient and observant to bring the trees back into production.
Although injury to foliage and young growth is visible within a few days of the fire, the full extent of the damage may not be known for several months or possibly the next growing season. In the case of severe injury, die-back may continue to occur for several months after the fire. New growth that occurs after the fire may suddenly collapse the following year when the growth is tested by Santa Ana conditions.
The important rule to follow after a fire is to do nothing - don't prune, don't water, don't fertilize. The avocado has a tremendous ability to come back from fire and frost damage. However, the tree will tell you where it is coming back. It will start pushing growth where the tree is still healthy. It may take 3 to 6 months for this growth to occur.
Delay pruning until the tree clearly shows where it is going to regrow. By waiting, you save the expense of having to return sometime later to remove more wood and also will be able to save the maximum about of tree.
In the meantime, if the tree has been defoliated by the fire, it has lost its ability to transpire water. Watering a tree with no leaves, will set up those conditions that are conducive to root rot. Until the tree begins to leaf out, the emitters should be capped or plugged. Then as the tree puts on new growth, shallow, infrequent irrigations should start. This may mean replacing the 10 gph microsprinkler with a 1 gph dripper if only a portion of the orchard has been burned and the rest of the trees need their usual amounts and frequency of water.
An activity the grower can perform is whitewashing. The defoliated tree can be further damaged by sunburn after it has lost its protective cover of leaves. The upper surface of horizontal limbs and the south sides of exposed trunks are the most affected. The whitewash can delay the appearance of new growth, but it does not affect total growth. There is usually no value in applying the whitewash to small limbs.
There are various commercial whitewashes on the market or one can be prepared by mixing 50 pounds of hydrated lime and 100 gallons of water. The easiest to prepare is the cheapest latex paint on the market mixed with water to the extent that it will go through a sprayer.
Avocado trees have a great ability to recover after fire damage. Even trees killed below the bud union will frequently develop into good trees if they are rebudded and given good care. Trees which do not put out vigorous sprouts should be removed. Interplanting avocados would rarely be advisable because of their rapid recovery. Think of fire as an advanced pruning plan.
- Author: Ben A Faber
It promises to be an outstanding seminar.
André Custodio Franco, assistant professor, Indiana University, Bloomington, will speak on "Deciphering the Soil Macrobiome: Belowground Communities Driving Ecosystem Responses to Global Change" at a seminar hosted Monday, Nov. 18 by the UC Davis Department of Entomology and Nematology.
It's set or 4:10 p.m. in Room 122 of Briggs Hall, UC Davis campus. It also will be on Zoom. The Zoom link:
https://ucdavis.zoom.us/j/95882849672.
His seminar will then be archived on the ENT seminar page.
"Growing scientific evidence indicates that soil fauna and the ecosystem functions and services they provide are threatened by global environmental changes such as those related to climate and land use," Franco says in his abstract. "These threats affect species diversity and functional groups in belowground food webs, impacting ecosystem services that all life depends on. A better understanding of global change impacts on interactions among soil fauna communities and plants, as well as on physical and geochemical processes driven by soil fauna will enhance our ability to predict changes at the ecosystem level."
He will discuss "recent evidence indicating that soil fauna responses may challenge aboveground-based predictions of ecosystem functioning under global change."
Franco joined the Paul O'Neill School of Public and Environmental Affairs, Indiana University in 2012 after serving as a research scientist at the Department of Biology, Colorado State University, from 2018 to 2022, where he was an International Presidential Fellow. Other honors include Senior Global Futures Fellow, Julie Ann Wrigley Global Futures Laboratory.
Franco focuses his research on how modern global environmental changes are affecting soils from tropical crop fields and rainforests to temperate grasslands, according to a faculty post. "His work has contributed to unraveling fundamental roles of microscopic soil animals, such as nematodes, and larger ones such as earthworms and termites, in influencing ecosystem responses to changing climate and land-use regimes."
His areas of interest include soil ecology, soil-plant interactions, ecosystem functioning, global environmental changes, sustainability and sustainable development.
Franco holds a bachelor's degree in agronomy (2008) from Universidade Estadual de Santa Cruz, Brazil; a master's degree (2012) in bioenergy, Universidade Estadual de Londrina, Brazil; and a doctorate (2015) in soil science from the University of São Paulo, Brazil. His dissertation: "Soil Engineering by Macroinvertebrates: Controls on Soil Organic Matter Storage Across Land Use."
Nematologist Amanda Hodson, assistant professor of soil ecology and pest management, is coordinating the ENT seminars. The full list is here. For more information or for technical issues, contact Hodson at akhodson@ucdavis.edu.
- Author: Ben A Faber
Confronted with approaching freezing conditions a grower has several options to mitigate the potential cold damage. There are foliar sprays like copper that can reduce the incidence and need to be applied several weeks in advance of cold. There are orchard heaters that are still allowed in some growing areas but tend to be expensive to run due to fuel costs. There are wind machines that are capable, but less effective on avocado hillsides that have natural air movement. Then there is irrigation.
Of course you need healthy, well-watered trees to protect, otherwise, it is probably not worth the effort. And you need water that is dispersed in the air. Drip is much reduced in efficacy compared to microsprinklers and much less than high pressure overhead sprinklers. And you need water volumes that can be used continuously over the protected area during the freezing period.
Using irrigation water in frost control is a delicate balance among different physical characteristics of water. When it freezes, from a liquid state to the solid ice state, heat is released. More than what is actually making up the temperature of the liquid water. But then, in its liquid state, it starts evaporating turning to a gas which cools the surroundings. Heat from liquid to solid and cooling from liquid to gas. There's another property of water which is that it conducts heat really well, better than solid earth. So, wet soil heats up better from the daytime sun than a dry one.
So, you want to make sure the soil is moist during the day to soak up the heat. Then, you don't want water being applied after sunset to avoid evaporative cooling. Then when the trigger temperature for freezing occurs, the system should be run continuously so that heat is released during the freezing cycle. If you stop the water, then evaporative cooling kicks in and it could be colder than it would be if you had not run the water. And sometimes the emitters freeze up if they are turned off, and then they don't function when you try to come back around.
So, with that, you need to decide how much water you can run continuously in a given area. So, what is the coldest spot, and can you cover that area continuously for the cold period? Or the reverse is, if you know the cold area is going to get really cold and it may not make it through the cold even with irrigation, what is the area you want to protect that you know can be helped with irrigation? The water needs to run continuously. You don't want to be turning it on and off in order to roll it over to other irrigation blocks. When the water is turned off, the air starts cooling from evaporation. So decide how much area can be watered with the given volume.
Knowing all this you start watching for the cold with low temperatures that show 32 or lower. Older trees with canopies to the ground can handle more cold than young trees with little canopy to retain heat. Watch for the dew point. If it shows something much below 32, like 25, that means the air is dry and there will be a rapid temperature drop once temperatures start heading for the low temperature.
So, you are forewarned. Get water on to the grove to make sure the trees are adequately hydrated. Then a couple of days before the freeze event, make sure the surface soil is wetted during the day to take advantage of daytime heat, but make sure the water is off before sunset. Then when the big night hits, when temperatures hit a trigger temperature like 33 or 34, you should start the water. You want to have the system going before it drops below 32. Run the system until sunrise, and then you can most likely shut down. And wait for the next night and follow the same drill. We often will have two to three nights in a row that need protection.
Hopefully there's enough water for successive nights. And hopefully, it's not so much that root rot becomes an issue. Isn't farming fun?
