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Plant Management – Page 2

2005 Craig Kallsen (Scion/Rootstock Incompatibility)

Scion/Rootstock Incompatibility as the Cause of Tree Decline in Fukumoto Navel

The objective of this research begun in 2003 is to explore scion/rootstock incompatibility as a possible cause of tree decline in Fukumoto navel. Tree decline in Fukumoto navel has been characterized by poor growth – especially of the scion – profuse sucker proliferation at the graft union, and sparse, yellow leaf canopies. The decline of some trees is common in almost all Fukumoto orchards on trifoliate or trifoliate hybrid rootstocks (i.e. citrange rootstock such as Carrizo and C-35), however the severity varies widely among orchards. Tree death has occurred in orchards, especially in some orchards planted on C-35, Carrizo or trifoliate rootstocks.

2008 John karlik (Measureing Ozone Removal)

Measurements of Ozone Removal and VOC Emissions in Citrus Trees with Implications for Regional Air Quality

This project was requested by the Citrus Research Board with an overall objective of understanding the relationship of citrus trees to ozone, the principal air pollutant in California airsheds. This project has two phases. In the first phase, measurements were to be made with citrus in an enclosure apparatus. In the second phase, citrus is to be measured in the field. The project is currently within budget and on schedule.

2008 Craig Kallsen (Scion Rootstock Incompatibility) 1

Scion/Rootstock Incompatibility as the Cause of Tree Decline in Fukumoto Navel Orange

Fukumoto navel produces fruit that matures early, has a deep orange color and round shape. However, many growers have encountered difficulties in growing this cultivar. Compared to other navel cultivars, a Fukumoto orchard will have a high percentage of stunted, low-yielding trees. The stunting is characterized bypoor growth of the scion resulting in a lowratio between the diameter of the scion compared to the diameter of rootstock, and a proliferation of scion sprouts at or just above the graft union. Stunting and decline of Fukumoto trees in growers’ orchards have occurred with citrange and trifoliate rootstocks. Decline symptoms include leaf yellowing, leaf drop and, in some groves, tree death. Declining trees are most obvious as the trees mature.

2008 Craig Kallsen (Irrigation Stress on Early Navels)

Irrigation Stress and Early-Navel Fruit Maturity

The objective of this research was to measure effects of late- season irrigation stress on fruit yield, quality, and maturity of an early-maturing navel orange variety. This report concludes four years of research funded by the Citrus Research Board.

2008 Bradley D Hanson (Simazine Degradation Patterns)

Assessing Simazine Degradation Patterns in California Citrus Orchards with Different Simazine Use Histories

Simazine (e.g. Princep) is a commonly used herbicide in California perennial crops including citrus, grape, stonefruit due to its broad-spectrum, long duration control of weeds, and relatively low cost. Although most herbicides are primarily degraded in soil by the activity of microorganisms, there have been reports of “rapid” degradation of some herbicides following repeated use of the same material due to the buildup of microbial populations that are able to use the herbicide as a carbon source.

2008 Abhaya Dandekar (DMS VOC Sensor for Citrus)

A Generalized Reagentless Sensor to Detect Citrus Plant and Fruit Responses

Rapid, early, and accurate diagnosis in the orchard is essential to counter a disease threat at an early stage of infection. Currently, diseases like HLB are diagnosed by scout teams looking for disease-specific visual symptoms, which often appear too late to prevent secondary spread. To be successful, early diagnosis must recognize the complex interactions of pathogen, insect vector, and host plant. Once the bacteria are systemic, it is too late to prevent additional spread of the disease by its insect vector the Asian Citrus Psyllid, Diaphorina citri (ACP). This project focuses on the analysis of the induced volatile organic compound (IVOC) emissions to enable the early identification of this or other citrus pathogens under field conditions.

2007 Lovatt and Chao (Efficacy of GA3 in Clementines)

Improving the Efficacy of GA3 to Increase Fruit Set and Yield of Clementine Mandarins in California

The Nules Clementine (Citrus reticulata Blanco) (also called ‘Clemenules’ or ‘De Nules’) is a seedless mandarin of great fruit quality. It is the leading Clementine cultivar produced around the world. In recent years, California growers have planted thousands acres of Nules Clementine and more may be planted in the future. . The oldest plantings of ‘Nules’ Clementine in California are now in production.

2007 Kallsen and O’Connell (Scion Rootstock Incompatibility)

Scion/Rootstock Incompatibility as the Cause of Tree Decline in Fukumoto Navel Orange

The most obvious symptoms of decline as encountered in commercial Fukumoto navel groves include overall stunting of the tree. The stunting is characterized by poor growth of the scion resulting in a low ratio between the diameter of the scion compared to the diameter of rootstock, and a proliferation of scion sprouts at or just above the graft union in citrange and trifoliate rootstocks.

2007 Kallesn and Sanden (Irrigation Stress on Early Navels)

Irrigation Stress and Early-Navel Fruit Maturity

In Year Two as in Year One, the objective of this experiment was to measure the effect of three irrigation treatments, beginning in early August, on yield and fruit quality factors of early-maturing Beck navel in the southern San Joaquin Valley of California. The experimental location continued to be ideal for water stress experiments in that rainfall from August through early November was minimal inYear 2.

2007 Bradley D Hanson (Simazine Degradation Patterns)

Assessing Simazine Degradation
Patterns in California Citrus Orchards with Different Simazine Use Histories

Simazine (e.g. Princep) is a commonly used herbicide in California citrus orchards where 27% of orange, 5% of lemon, and 6% of grapefruit acres are treated annually (USDA-NASS 2004). Simazine also is an important weed management tool in other California orchard and vine crops, particularly in grapes where simazine is second only to glyphosate in total pounds of active ingredient used. Herbicides containing simazine have been used for many years in orchard and vine crops because of broad-spectrum weed control, long duration of weed control, and the relatively low cost of the material.