Posts Tagged: lemon
Article written by UC Davis PhD student Caio Brunharo from his dissertation research. It was originally posted in the September 2017 "Weed Management Notes" newsletter from the UC Cooperative Extension office in Glenn County by new weed science and agronomy Farm Advisor Mariano Galla (also a UCD PhD student in weed science!).
Take care, Brad
Italian ryegrass management in perennial crops in California
Caio Brunharo1 and Brad Hanson2
1PhD Candidate, UC Davis; 2UCCE Weed Science Specialist, UC Davis.
Italian ryegrass (Lolium perenne L. spp. multiflorum (Lam.)Husnot) causes yield losses in a variety of cropping systems around the world (Figure 1). This species is highly competitive with annual crops but may also compete with perennial crops particularly during the establishment years when they are most vulnerable to direct competition. In orchards and vineyards, ryegrass infestation can also interfere with cultural practices during the bearing years.
Repeated herbicide use has selected Italian ryegrass populations resistant to a variety of herbicide mode of actions across the world. Glyphosate-resistant Italian ryegrass populations were first reported in California in 2008, and the evolution and spread of these populations in the state made alternative postemergence herbicides an important management strategy against this troublesome species.
Recently, poor control of Italian ryegrass with Gramoxone 2.0 SL was reported in a prune orchard near Hamilton City, California. Greenhouse dose-response experiments and field trials were carried out to evaluate Italian ryegrass response to several postemergence and preemergence herbicides.
Our greenhouse studies confirm that the Italian ryegrass population from Hamilton City is resistant to Gramoxone 2.0 SL, Envoy Plus, Roundup PowerMAX and Osprey, whereas Fusilade DX, Rely 280, Simplicity CA, Matrix and Poast controlled both a known-susceptible and resistant Italian ryegrass population (Table 1). (note: Osprey and Simplicity CA, which are not registered in perennial crops, were included in the study for comparison purposes). Our criteria were that whenever the resistance index (RI) was larger than two and the comparison between biotypes was statistically different (P <0.05), the population was considered as resistant to that particular herbicide. Matrix is an exception, however, because this herbicide controlled both biotypes at well below its recommended field rate.
The field experiment with postemergence herbicides corroborates with data from the greenhouse studies, since glyphosate and paraquat did not adequately control the herbicide-resistant population from Hamilton City. On the other hand, most of the treatments containing Rely 280 were effective for control of the resistant population (Figure 2).
From the preemergence herbicide trial, all treatments containing Alion controlled the resistant population up to 150 days after herbicide application. Chateau, Surflan AS, GoalTender, Prowl H2O, and the tankmixes of Chateau + Prowl H2O and Chateau + Surflan AS exhibited control percentages above 90% with long lasting residual activity (up to 150 days after treatment; Table 2).
Even though several postemergence herbicides controlled Italian ryegrass in our research, it should be noted that ryegrass populations resistant to Fusilade DX, Rely 280 and Poast have been reported elsewhere in the state (data not shown), and overreliance on these herbicides will increase the chances of selection of further cases of resistance. A chemical weed management program in areas infested with Italian ryegrass should include a preemergence herbicide with long residual sprayed in the winter (Alion, Chateau, Surflan, GoalTender or Prowl H2O are possible options) tankmixed with an effective postemergence herbicide. In areas where herbicide-resistant weeds are known to be present, alternative herbicide chemistries should be adopted (rather than increasing the herbicide rate sprayed) in both the winter and spring application. In some cases, a short residual grass herbicide included with the post-harvest burndown application may help reduce recruitment of early-germinating Italian ryegrass plants which will reduce weed pressure and densities to be managed later in the season.
0University of California Cooperative Extension Area-wide IPM Advisor, Kearney Agricultural Research and Extension Center, Parlier, CA
Leaffooted Bug Populations in Ventura County - 2017
Cold winter temperatures can reduce populations of leaffooted bug, Leptoglossus zonatus (Dallas), by ~50 to 80%. But unfortunately, it takes a cold year much like occurred in January of 2007 when daytime temperatures remained low and nighttime temperatures reached about 20° F for several hours. In other words, ouch for the citrus crop. Fall and winter temperatures of 2016 / 2017 were ideal for leaffooted bug and the 2017 growing season started out with large populations. I need to add that we do not fully understand if the wet winter positively affected populations - it certainly did not have a negative impact. Moreover, it appears that leaffooted bug populations going into later 2017 will be very large.
Monitoring and managing leaffooted bug presents an IPM challenge. In the fall between September and mid-November, the species produces a full generation; certainly, on pomegranate and although I have not observed it, also on desert willow. In most years, adults move from those host plants by late December to protected overwintering sites such as Mediterranean fan palm and Italian cypress trees; and perhaps citrus. In early March leaffooted bug leave overwintering sites to feed on what happens to be available at the time. In the San Joaquin Valley and the Sacramento Valley region it is almonds and pistachio. In other parts of California, where those nut crops are not available, citrus may be an important host crop. In Louisiana, for instance L. zonatus can cause considerable economic damage on satsuma mandarins, however in California the species has not been reported as a serious pest on any of the citrus cultivars.
The IPM challenge is that we do not have an effective monitoring tool to detect the bug when they leave overwintering sites. And moreover, once leaffooted bug is detected, no economic threshold exists , and pyrethroids offer the best management option – not necessarily the best IPM option.
Given the importance of pomegranate in the life cycle of leaffooted bug, PCAs and growers need to concentrate monitoring efforts on that crop during September through October, especially focusing on unmanaged orchards and hedgerows. If populations are found they will consist mainly of immature stages and there are two management options, clothianidin and pyrethrins. The caveat is that those compounds have only contact activity; coverage must be good and the insecticides will likely not have a great impact on adults because they will spook and fly away before being sprayed. Two organic compounds, pyrethrin (PyGanic) and Beauveria bassiana Strain GHA (BotaniGard) can also be effective. But again, those compounds have no residual activity so the spray must contact the bugs to be effective.
Insecticide use should occur only if monitoring indicates the presence of leaffooted bug and/or its feeding damage. Apply insecticides only after considering the potential risks of the compound to beneficial organisms, including bees and biological control agents, and to air or water quality. For more information on these topics please consult the UC IPM Pest Management Guidelines for Almonds at http://ucipm.ucanr.edu > Agricultural pests > Almond
(Ben: This insect became prominent in Ventura in 2015. Kris was minding his own business when he saw this bug traveling at 50 mph down the road.
Fig. 1. Aggregation of leaffooted by on pomegranate in early October of 2016. The aggregation is comprised mostly of fifth instar.
Fig. 2. Adult leaffooted bug on pomegranate in Ventura County, September 8, 2017.
Gopher Snakes (Pituophis catenifer), known as a constrictor snake, are one of the most commonly seen snakes in California. Mainly active during the day, they are active after sundown on hot days. They are often observed crawling across trails and roads, especially in the morning and evenings when daytime temperatures are high. They live in diverse habitats and are regularly seen around human residences, including suburban backyards and in agriculture commodities as they are attracted to the rodents which thrive in those areas. The gopher snakes help growers control their pest problems by preying on rodents, rabbits, and birds that would otherwise destroy or ruin crops and yields. When the weather turns hot, they hunt during the night and rest on warm rocks or pavement during the day. They hibernate during the winter and are out and about between April and October, however in Southern California because of the warm climate their presences is more consistent.
Gopher Snakes are large and heavy-bodied reptiles - reported to reach 9 feet (275 cm) in length, but 4 feet (120 cm) is more common. The underside is creamy or yellow, often with dark spots. Unfortunately, this harmless and beneficial species is very often killed out of fear that it is dangerous or that it is a rattlesnake. Since the patterns on their backs are similar to rattlesnakes and because they coil, vibrate their tails, and even strike when threatened. Other differences include: gopher snake tails taper to a thin tip and lack rattles; rattlesnake tails always have rattles (or immature buttons), unless the rattle has broken off, gopher snake heads are usually narrow, while rattlesnake heads are always triangular, and gopher snake eyes have round pupils, while rattlesnake pupils are vertical.
So, if you see a Gopher snake in your grove, its best to leave him alone so that it can contribute to your Integrated Pest Management plan.
Leafminer, sometimes Leaf Miner. It's that time of year. Those little moths come out in the late afternoon and flit about. They lay their eggs and when they hatch the larvae start burrowing through the leaf. The recent heat and also the generally warm summer have set them off. And it is obvious now. The heat has exacerbated the collapse and drying of the leaves and on older trees it looks like trees have been decorated with a sprinkling of light brownish ornaments. It is disturbing. But it's not the end of the world, like …………ACP can be.
Leafminer adults are tiny moths less than 0.12 in long (2 mm) with wings span twice as wide.
Pretty shocking from a distance
Citrus leafminer larvae feed by creating shallow tunnels, referred to as mines, in young leaves. It is most commonly found on citrus (oranges, mandarins, lemons, limes, grapefruit and other varieties) and closely related trees (kumquat and calamondin). The larvae mine the lower or upper surface of the leaves causing them to curl and look distorted. Mature citrus trees (more than 4 years old) generally tolerate leaf damage without any effect on tree growth or fruit yield. Citrus leafminer is likely to cause damage in nurseries and new plantings because the growth of young trees is retarded by leafminer infestations. However, even when infestations of citrus leafminer are heavy on young trees, trees are unlikely to die. But they can sure struggle pushing new leaves that then get attacked anew.
Several years ago, we did a trial where we sprayed mature trees with leafminers every month for 18 months with a rotation of different chemicals and even the most heavily treated trees had some damage on them. The most heavily infested trees looked horrible, but in that period of time there were no lemon yield differences. Young trees treated with a systemic were able to free themselves of infestation. This has been commented on by others, that soil applied systemics on heavier soils can have problems controlling leafminers.
Photos: Tunnels and the rapidly dried leaf after a heat spell
SACRAMENTO — The California Department of Food and Agriculture (CDFA) and the United States Department of Agriculture (USDA) have established a 94-square mile quarantine in portions of Riverside and San Bernardino counties following the detection of the citrus disease huanglongbing (HLB), or citrus greening, in a single citrus tree in the city of Riverside. HLB is a deadly disease of citrus plants and closely related species, and can be transmitted from tree to tree by the Asian citrus psyllid.
The quarantine boundaries are on the north, Interstate 10; on the east, Box Springs Mountain Reserve; on the west, Riverside Municipal Airport; and on the south, East Alessandro Boulevard. HLB quarantine maps for Riverside and San Bernardino counties are available online at: www.cdfa.ca.gov/plant/pe/InteriorExclusion/hlb_quarantine.html. Please check this link for future quarantine expansions in these counties, should they occur. Quarantines are already in place for HLB in portions of Los Angeles and Orange counties.
The quarantine will prohibit the movement of all citrus nursery stock out of the area, while maintaining existing provisions allowing the movement of only commercially cleaned and packed citrus fruit. Any fruit that is not commercially cleaned and packed, including residential citrus, must not be removed from the property on which it is grown, although it may be processed and/or consumed on the premises.
Residents are urged to take several steps to help protect citrus trees:
- Do not move citrus plants, leaves or foliage into or out of the quarantine area, or across state or international borders. Keep it local.
- Cooperate with agricultural crews placing traps, inspecting trees and treating for the pest.
- If you no longer wish to care for your citrus tree, consider removing it so it does not become a host to the pest and disease.
CDFA crews have already removed the infected tree and are in the midst of a treatment program for citrus trees to knock down Asian citrus psyllid infestations within 800 meters of the find site. By taking these steps, a critical reservoir of the disease and its vectors will be removed, which is essential to protect the surrounding citrus from this deadly disease.
HLB is a bacterial disease that attacks the vascular system of plants. It does not pose a threat to humans or animals. The Asian citrus psyllid can spread the bacteria as the pest feeds on citrus trees and other plants. Once a tree is infected, there is no cure; it typically declines and dies within a few years.
CDFA, in partnership with the USDA, local county agricultural commissioners and the citrus industry, continues to pursue a strategy of controlling the spread of the Asian citrus psyllids while researchers work to find a cure for the disease.
—California Department of Food and Agriculture
Over 20 new trees in Southern California have been confirmed HLB-positive. The new finds raise the total number of trees with huanglongbing disease found in California to around 100. All of the trees found in the state have been located in residential areas.
The Citrus Pest and Disease Prevention Program (CPDPP) issued a press release that stated 21 trees in Anaheim, and four trees in Pico Rivera tested HLB-positive. The CPDPP, a program of the California Department of Food and Agriculture (CDFA), stated the current quarantine in Southern California would be slightly expanded in Orange and Los Angeles Counties.
The new detections were found due to intensive surveying that's part of the response program. Highly trained crews sample trees where HLB-positive Asian citrus psyllids have been found. CDFA says their Sacramento facility can process 10,000 samples a month.
All of the detections in California have been residential trees. The CPDPP is currently running an outreach program that involves public service announcements, coordination with officials, and large public events in the quarantine area. The goal is to educate residents on the disease and the insect that spreads it. Go to the CPDPP website to find out more about the disease, insect, and quarantines.
Photo: HLB symptoms