Apr 3, 2015
Growing tomatoes a humbling experience

Tomatoes can be a very challenging to grow commercially. Managing nutrients, diseases, and insect pests all contribute to this annual test of our spirits. If it was not for the high potential for profits few would grow tomatoes.

After growing tomatoes for research since 2000 and acting as an Extension Educator since 1997, it is clear that growing tomatoes commercially is an annual challenge. Whenever I start to feel like I’ve got this crop figured out, a new problem arises. Early on in my trip down tomato lane there was learning to manage yellow shoulders and blossom end rot. Later on it was boron and other micronutrient deficiencies and toxicities. More recently, the move into high tunnels has brought Leaf Mold to front and center. It is a very good thing that tomatoes have such high revenue potential or no one would grow them.

First, why do we grow fresh market tomatoes? Whether in high tunnels or in the field, no crop has a greater potential for revenue per acre than tomatoes. Assuming a field population of 4,840 plants per acre (43,560 ft2 / rows 6′ apart, with plants spaced 18” apart in the rows) and a conservative yield of 20 lbs. of fruit per plant, it is very possible to get yields of 3,800 25 lb. boxes of tomatoes per acre. Assuming a low auction price of $15 per box, even modest yields can generate in excess of $57,000 per acre. Since high tunnel tomatoes are 3-4 weeks earlier than the field season, are of higher quality and often produce much higher yields per plant, gross revenues per plant from a tunnel are often much higher on a per square foot basis than field culture. When you factor in direct market sales and specialty tomatoes such as grafted heirlooms it becomes clear that tomatoes are worth the effort.

Choosing what variety or varieties to grow is one of the most important decisions that a grower can make. Modern determinate hybrids such as Red Deuce, Red Bounty, Red Mountain, Scarlet Red, and Primo Red each bring with them specific characteristics that impact production and marketing. 2014 was a banner year for Leaf Mold (Passalora fulva) in high tunnels. Usually this disease is limited to the lower leaves which can be readily removed from the plant up to the first fruiting cluster. In 2014, clients brought samples of plants that were completely covered from the bottom leaf to the top of the plant. As I looked at the infected plant samples I wondered if I was looking at a new more virulent strain of the disease, a varietal susceptibility issue, or just an abnormally bad season. A PVMRP research project for 2015 housed at the Penn State Southeast Agriculture Research and Extension Center will seek to identify which determinate red slicing tomatoes have resistance to Leaf Molds.

While Leaf Mold management can be a real problem for high tunnel growers, it’s the bacterial diseases that had the greatest impact in 2014. While Bacterial Spot and Speck can greatly reduce fruit quality, it’s Bacterial Canker that can decimate your fields. Bacterial Canker was a huge problem in 2014 throughout much of PA and the Mid-Atlantic in spite of greater use of hot water seed treatment. The best advice for tomato growers going into 2015 is to plan your disease management program as if bacterial diseases will strike:

Treat tomato seeds using hot water baths and closely follow all protocols for time and temperature.
Purchase plants only from reputable sources that hot water treat their tomato seeds.
Keep your propagation areas pristine. Never store cardboard boxes under benches. Keep hose ends off of the floor. Remove dead or damaged plant tissue from the area. Keep potting media covered when not actively filling pots or trays.
If reusing plastic trays, start off by hosing off all visible organic matter, then soak them in a solution containing a registered sanitizing agent containing chlorine, quaternary ammonia salt, or a peroxide based sanitizer per label directions.
Plant into fields that have not had bacterial disease for at least 3 years (longer is better).
Use a very proactive disease management program that includes Actigard, Regalia, coppers, mancozeb and crop stimulants such as GreenStim, Kalibor or Stimplex. Various combinations of these materials helped to keep plantings alive and harvestable in 2014 that had Bacterial Canker within the field.
Scout your fields and tunnels early and often for signs of disease and cull plants if necessary.
Pressure wash sprayers and tractor tires between uses especially after applications in suspect fields. In the same vein, disinfect all tools and rubber boots between fields.
If using wooden stakes, always use new stakes in your tomatoes. Reuse them in peppers or other crops next year, but the value of tomatoes easily allows for the use of new stakes. It is nearly impossible short of kiln drying your tomato stakes to completely kill all bacteria on them.

Tomato growers hold an annual battle with Yellow Shoulder and Blossom End Rot. Getting the right balance of potassium, calcium, and magnesium while still maintaining sufficient nitrogen for good plant growth is key to reducing culls from these disorders. Writing that is much easier than actually implementing it in the field or tunnel. Growers must start with a preplant soil test, apply sufficient nutrients to produce an ample crop, then monitor and adjust tissue analysis nutrient levels from before the first blossoms appear with fertigated liquid or soluble fertilizers.

The pH and alkalinity of your irrigation water greatly impacts tomato plants’ (peppers too) ability to take up nutrients from the soil solution. Tomatoes grow best at a pH range of 6.2-6.5. Most growers removing water from limestone-based aquifers need to inject acids in order to reach this pH range. Since the pH scale is a base 10 logarithmic scale, even seemingly small changes in the pH number are actually large changes in actual pH.

Western Flower Thrips (WFT) a vector for Tomato Spotted Wilt Virus, have become public enemy #1 for tomato growers. Their rapid reproduction rate, love of tomatoes, coupled with resistance to our most commonly used insecticides, make WFT arguably our most serious insect pest.

Every year is a bit different. 2013 was a major year for WFT in field-grown and high tunnel tomatoes while in 2014, generally only greenhouse and high tunnel growers had damaging populations. WFT are largely resistant to most common insecticides, so growers should look to biological control to manage these minute pests. To be successful with biocontrols growers must become acquainted with the nuances of managing and utilizing populations of beneficial insects and mites in concert with biopesticides in the field, tunnel and greenhouse. When you factor in managing spider mites, several species of aphids, whiteflies, and the occasional lepidopteran pest the task of keeping your tomatoes healthy and productive seems to get ever more complicated.

The big question for the 2015 season is which challenge or challenges will teach us once again that tomatoes are a most humbling crop. Every time that we get a handle on one major hurdle another is always lurking nearby. Soil and tissue test well and often, scout your crops regularly, practice IPM, pay attention to the Late Blight reports and be proactive in all things regarding tomato management.

Steve Bogash, Penn State Extension

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