November 17, 2008
The fungi known as Fusarium live in the soil which is why house plants, landscape and vegetable plants wilt, rot and die from the roots up. However, some plants which we would probably like to see their demise in the garden that may actually act as a fusarium disease host.
These “weeds” do not not seem to have any problems with the fusarium fungi but like to “share it” with other plants. The tall morning glory and the ivyleaf morning glory appear to be 2 of the fusarium carriers.
January 21, 2008
As the season for whiteflies approaches (and may be in full swing in certain areas), we should take a practical look at some of the decisions and plans of action we should take. This is above and beyond selecting which pesticide and how to zap them and control try to achieve control as we have been doing for the past few years.
Much has been written and said about how best to control whiteflies and a lot of it is very good advice. But do we end up following that advice, or just go ballistic when they really do appear.
Immediately, we try to control them with large quantities of whatever our chemical salesmen, crop advisors and colleagues say will knock them out? Generally, more of the latter, than the former.
I am not going to get into what chemical(s) works best or better or not at all. I’m going to leave that up to the experts and formulators.
My approach to this whole thing is to PLAN AHEAD, and we can do so by covering the following points:
Know your adversary: Be familiar with the life-cycle of the whitefly and the various stages it goes through and how those stages affect your crops.
This is very important and you must keep this in mind at all times.
The larval stage is the most damaging to the plant because it is when the insect actually eats and damages the foliage. Larva feed mainly on the undersides of leaves so it makes no real sense to spray over the top, now does it? And larva can be controlled but with only a very small portion of the “arsenal” labeled for whitefly.
Of course the easiest to control are the adults. Most insecticides available are indicated for knocking down the adults. Adults will lay their eggs mainly on the undersides of the leaves and in protected areas. If you want to control them, you should think of a product that will have residual effect and apply it on the undersides and not over the top.
The residual effect (the active ingredient staying potent on the surface for several days after application) will deter future visits to that area by adults that are looking for a good place to lay their eggs. You can also achieve this effect with certain spray oils and soaps, but application is the key to your success with whatever product you use.
Over the top spraying will help, but not give you good control.
And now the eggs. The adults will lay scores of eggs, mainly in the venal recesses of the underleaf epidermis. These eggs are not really affected by most insecticides.
Ovicides and a few bio rationals mainly derived from Beauvaria Bassiana will have a destructive effect on them, but again, application is the key.
Since these are all contact materials, they must touch the target to do any damage. And you must make sure you achieve that coverage, otherwise you’re throwing money and effort down the drain.
Resistance is also a very important factor in your planning. We have noticed that the adults mainly, develop resistance to certain ingredients, especially when those are being widely used and continually used in the same area.
We now hear that there may be a resistance problem with the “Silver Bullet” Imidacloprid, and this is mainly due to its extensive and continuous use as most growers found it to be a very effective preventive material.
Consequently, you should be on your toes and do some preliminary testing on the first colonies you get to assure yourself that the materials you will be using will be effective. Don’t wait until you have an infestation and then hit them with something that you will later realize (when it is too late) that they are resistant to.
If Imidacloprid works for you, remember that it has a relatively short effective period (21 to 28 days in vegetables) and therefore you will want to schedule it when it will be most effective in your particular plant’s growing cycle.
If you are growing a 3 month ornamental and don’t at the time of potting have whitefly pressure, you should wait and apply it (in whatever way recommended) when the colonies are threatening, which could even be in the latter stages of the plant’s production cycle.
Scouting is your best defense against whitefly damage. I’m not saying you won’t get them in your crop, but advanced notice of their presence will be a great help to your control program.
Also of great help will be to have your program in place so that you don’t have to be running around like mad trying to get the materials of setting up the sprayers and other equipment.
As far as thresholds are concerned, don’t wait to have three or more adults per plant. Swing into action with your prevention program when you first spot them. Remember, if you can stay ahead of them, you will be the winner.
Monitor fields around you, especially to “windward”.
Whitefly blow in with the wind, and if you are unfortunate enough to have a field of eggplant to windward of you, you are going to get a lot of visitors. Talk to your colleagues that are located around you and share all the information with them.
You alone will not be able to control this, but if all your neighbors get together and act on it, the insect pressure will be considerable lower and it will work out to everyone’s benefit.
Remember that the pressure of whiteflies will increase when you come out of the rainy season and go into a dry spell. Adults that normally would live in other vegetation surrounding you will move out of it when it dries up and seek green, tender, irrigated leaves. This should also be a warning to you.
Remember: Plan Ahead, Scout, Know Your Enemy, Apply Effectively, Work with your Neighbors and……cross your fingers and hope for the best!
December 31, 2007
TYLCV causes more severe symptoms and greater yield losses than Tomato Mottle Virus (ToMoV). It takes an estimated 15-30 minutes of SWF feeding to inoculate a plant. The SWF retains the virus, for several weeks. Symptoms will be visible in tomato in approximately 2-3 weeks after infection, a little longer than ToMoV.
Leaf symptoms include chlorotic margins, small leaves which are cupped, thick and rubbery. Tops of infected plants may took like a head of broccoli. The majority (up to 90%) of flowers abscise after infection, thus few fruit is produced. (TYLCV is very similar in its effects Bean Golden Mosaic Virus in that if young plants are affected, it is highly likely that fruit will not set).
TYLCV can affect more hosts than ToMoV, although crop plants are not considered with the exception of tobacco, which, like many of the weed hosts, do not show symptoms.
In Israel, weed hosts bridge the gap between tomato seasons. In the Dominican Republic, there is a government enforced whitefly free period. In Florida, we do not yet know the extent that weeds are a host, as many of our weeds do not grow in some of the countries where TYLCV is found.
This virus is not seed or mechanically transmitted. Whitefly transmission, however, is more efficient than for ToMoV. In greenhouse tests, 15 SWF were required for transmission, compared to 40 from ToMoV. Individual insects transmitted at 30-40%, compared to 5-10% for ToMoV.
Recommendations For Management
- Keep whitefly populations low especially in the first half of the season
- Use Admire in the transplants as soon as possible
- Use chemical control on all plantings of tomato and continue through final harvest and u-pick
- Isolate cherry tomato fields from large fruited plantings
- Delay fall plantings as much as is economically possible
- Learn to identify early symptoms of TYLCV and rogue Infected plants as soon as infections are identified throughout the season
- Pull plant from the bed and place in plastic bag at site, tie shut to prevent spread of any whiteflies to other plants, and discard in trash
- Plow under fields immediately after harvest to reduce whitefly populations and virus carry-over to the spring tomato crop and to other crops which are good hosts for whiteflies, and use the best sanitation practices
- Destroy volunteer tomato plants in and around fields
- Separate plantings of tomatoes in time and space from plantings of crop hosts which are good sources of whiteflies (ie. cabbage, cucurbits, potato)
- UV-reflective mulches will reduce landing of whitefties in your field and will help reduce incidence of both aphid and whitefly borne viruses including TYLCV.
- Destroy tomato volunteers throughout the season
- Delay spring plantings as long as is possible
- Use WF and virus free transplants
- Leaf symptoms: Chlorotic margins, leaves very small and cupped, thick and rubbery
- Plant symptoms: Stunting, more severe than that caused by ToMoV, like ToMoV, severity increases the younger the plant at infection; tops may look like broccoli
- Fruit symptoms: Majority of flowers abscise after infection, few fruits produced
- Host range: Broad
- Weed hosts: Unknown, but likely
- Whitefty transmission efficiency: In greenhouse tests 15 insects for 100% transmission; individual insects transmitted at 30-40%
- Seed transmission: No
- Mechanical transmission: Not under normal conditions