Viruses vectored by insects 
 
We are on the final section of virus transmission. Virus transmission by insects is one of the most efficient and economically important transmission in agriculture. When you have insects in your crops, not only you are losing your crops because of feeding/chewing by insects, a lot of insects also act as a vector of plant viruses. 
 
Seven out of 29 orders of insect feeding on living green land plants are vectors of plant viruses. 
Insect transmit viruses in 4 distinct modes: 
 

1. Non persistent transmission: The insects can acquire the virus in a matter if seconds/minutes and they are immediately viruliferous. The virus in retained in the stylet of the insect and are transmitted to the next plant the insect feeds on. The virus is retained in the vector only for few minutes and is lost after insect molting. Most viruses transmitted by aphids are non persistent. So when you see few aphids in your melon field and see cucumber mosaic virus symptoms 1-2 weeks later in your field, don’t be surprised. Aphids are efficient vectors, and since viruses are systemic it takes anywhere from few days to 2-3 weeks for the plants to show symptoms. Thus it is very important to manage insects in the field even if you don’t think the ‘pressure’ is not as high. 

Viruses transmitted in non-persistent manner:
 Papaya ringspot virus 
Zucchini yellow mosaic virus 
Watermelon mosaic virus

1. Semi-persistent transmission: The insects can acquire the virus in minutes/hours and there is no latent (incubation) period in the insect. The virus can stay in the insects foregut for hours and is lost after insect molting. Some species of aphids and whiteflies fall in this category.  Example: Cucurbit yellow stunting disorder virus in melons transmitted by whiteflies. 

1. Persistent circulative: Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus for weeks. Virus can be present in the vectors hemolymph but there is no multiplication of virus in the insect body. Vectors in this transmission includes: Aphids, leafhopper, whiteflies, treehopper. 

Example: Beet curly top virus transmission by beet leafhopper 
 

1. Persistent propagative:  Insects have to feed on virus infected plants for hours/days to acquire the virus and the virus has to incubate for hours/days in the insect. After insect can transmit the virus throughout its lifespan. The virus can multiply in the vector system and often times the virus particles are also passed on to the insect offspring. Tomato spotted wilt virus is transmitted on persistent propagative manner by 9 different species on thrips. 

Save the Date : 2024 Plant Pathology Workshop 
When: August 29^th 8AM-12 PM ( breakfast and Lunch provided by Gowan Company and BASF) 
Where: Yuma Ag Center, 6425 W 8^th Street 
What will covered: Plant Pathology program Updates, past season field trial results (we
have some exciting results to share), Q&A to help better Plant pathology program,
Industry panel discussion for all your industry related questions! See you in few weeks! 

Glyphosate is the most widely used herbicide in Arizona, the USA and worldwide. That may be coming to an end and it is probably not too early to start to consider alternatives. Glyphosate was developed in the early 60’s as an industrial solvent to clean pipes and boilers. Monsanto registered it as a herbicide in 1974 and sold it for around $100/gal. It now sells for $30 to $50/gal and is used by people everywhere. It has fallen in popularity in recent years for a couple reasons: 1) A couple lawsuits were decided last year in favor of a groundskeeper and a  homeowner who claimed they had contracted cancer as a result of glyphosate use and thousands of similar lawsuits are now underway even though the EPA has found it to be safe., and 2) More than 40 separate weed species have been identified that have developed resistance to Glyphosate over the last 40 years. This has caused serious problems in many parts of the country. Only one species, palmer amaranth, has been identified in Arizona and careful management is needed to avoid more. Some counties and some municipalities have already banned the use of glyphosate. The reason why Glyphosate is so popular in commercial agriculture are that 1) it is systemic and effective on most weeds including those that have become well established, 2) It is used postemergence to the weeds and has little soil residual activity and will not hurt most crops that are planted soon after application and 3) it has been off of patent for several years is relativity affordable and 4) It is not volatile and will not drift to sensitive crops in the vicinity There are not many herbicides that have these same characteristics. There are several contact herbicides that are broad spectrum with little soil residual and are not volatile, but they are normally only effective on small seedlings Several are used in combination with Glyphosate, but they are can be inconsistent when weeds get beyond the seedling stage. These include bromoxynil (Buctril, Maestro), Paraquat (Gramoxone), Pyraflufen (ET), Carfentrazone (Aim, Shark) Caprylic acid (suppress), Pelargonic acid (Scythe) and others. Some have soil activity (Goal and Chateau). The Plant growth regulators like Dicamba (Clarity), 2,4-D and MCPA are volatile and dangerous to use around many crops. We will be conducting trials this year to find alternatives to that are used postemergence and have the same characteristics as Glyphosate. Our trials will focus on postemergence weed control, soil residual and volatility. So far, our list is fairly short and includes Glufosinate, (Rely, Liberty, Finale, Cheetah), Indaziflam (Alion, Specticle, Marengo), and Pyroxasulfone (Zidua), We would like suggestions so that we can expand this list. Please contact myself (btickes@ag.arizona.edu) or Marco (marco@ag.arizona.edu) if you have suggestions.