Pests, Pathogens, and too Little Phosphorus

Before planting, California lettuce fields are often chemically fumigated to get rid of Nematodes. Chuck and I wish that the public were made aware of the major differences between buying field lettuce and our purer, crisper, hydroponic varieties.

In addition to Nematodes, lettuce grown in soil is prone to a number of other major pests. Black Cutworms, Beet Armyworms, the Cabbage Looper Caterpillar, and the Corn Earworm plague field-grown lettuce crops.

Aphids, Mites, Thrips, and Whiteflies can also infest greenhouse-grown lettuce, but only if common sense sanitary procedures are ignored. As well, Chuck and I make sure that our four greenhouses are equipped with fine-mesh screens at every opening, to make sure that flying insects do not invade our bread and butter crops.

Two species of Aphid especially like to munch on lettuce. The Potato Aphid (Macrosiphum euphorbiae) and the Green Peach Aphid (Myzus persicae) feed on plant sap found in lettuce leaves and their feeding habits will certainly reduce plant vigor.

These Aphids may vector the Lettuce Mosaic Virus (LMV) and introduce toxins into plant tissue which may necrotize the tissue in that particular area. Aphids also excrete a honey-dew-like substance that attracts ants to soil-grown plants.

Since both Chuck and I are committed to Integrated Pest Management (IPM)—meaning that we choose to exhaust every natural method of disease and pest prevention, before we would ever consider the use of chemicals to fight or prevent infestations—we prefer prevention to allowing a problem to invade our greenhouses.

Barricade is usually the first product to go into our Nutrient Pond pre-mix tank, since it takes a while to dissolve. Many growers mix it in hot water and shake it vigorously, and still pour it in the night before so it can blend into the other ingredients of our nutrient solution.

Barricade is a potassium silicate product which fortifies the cell walls of our lettuce, pak choi, and herbs. Stronger and thicker cell walls are able to withstand potential assaults by insects or pathogens much better than unfortified cell walls.

Another product that we use both as a foliar spray and a root zone additive is Scorpion Juice. This Advanced Nutrients formula imparts an induced systemic resistance to all our plants which is akin to giving them an immunization prior to any harmful microorganisms or parasitical insects making contact with our produce.

One year the Aphid infestation was so great in our original greenhouse, the one that grows Boston Lettuce, that we purchased a quantity of lady beetles and tiny wasp parasitoids to help us get rid of the Aphids. Natural predators work much better in a greenhouse setting rather than out in the field, where they can scatter and thus be ineffective.

Any kinds of pests or diseases have to be dealt with prior to harvest. I never forget biting into an apple when I was a child and being greeted by a cheerful green worm coming out of the apple’s core. It was an organic apple, no doubt, but allowing a parasite or a malady to proceed with your produce to your customers is a sure-fire way to lose them.

A word about Protector is appropriate here. This AN product was reintroduced recently after sales of it were stopped for a time, while the company negotiated with the government whether or not it was a fungicide.

Designed to fight and prevent Powdery Mildew, Protector is a highly effective product but it is not a chemical fungicide. So now it’s back on the market and it is very useful to have in our arsenal, especially during the potentially high humidity of the summer months.

Protector is accompanied by a word of caution. For flowering plants, do not spray after week 2 of bloom. For plants that will be consumed, such as our lettuce, pak choi, and herbs, do not spray within a few weeks of harvest.

It seems that Powdery Mildew needs a specific pH range to thrive and survive. The potassium bicarbonate in Protector changes the pH of the surface of your plants, making it an inhospitable place for this insidious fungus to grow.

However, the same properties that cause the pH change could also alter the colors of your flowers or impart an odd taste to your consumables. So be forewarned and use Protector wisely.

I recently came across an eye-opening statistic. A pound of lettuce contains 95% water, 56 calories, 3.9 grams of protein, 0.3 grams of fat, 86 milligrams of Calcium, 2.2 milligrams of Iron, 1,420 milligrams of Vitamin A, and 54 milligrams of Ascorbic Acid, otherwise known as Vitamin C.

Optimum lettuce growth occurs between 60 and 70º F (15 to 20º C) but the night temperature has to be kept much cooler in order to ensure the production of good quality lettuce.

Another trick of making sure that the lettuce you grow is of good quality is feeding your crop the best fertilizer available in just the right quantity. Studies have shown that using too little Phosphorus will reduce lettuce yields, for instance.

Using too much fertilizer—feeding your lettuce too often—may result in a soluble salt buildup. This could have phytotoxic effects on plant growth, you could pollute the groundwater in your area with your discharge, and your budget will suffer since you’re paying for unnecessary plant food.

By using a scientifically measured amount of plant nutrients, clearly explained and demonstrated by the Advanced Nutrients Nutrient Calculator, my partner and I avoid the obvious pitfalls of too much or too little. Our basic fert is the AN 3-part, Micro, Grow, and Bloom, only without the Bloom for obvious reasons.

Lettuce has low salt tolerance. Soluble salt injury is manifest in poor germination and the diminished size of the harvested heads. We try not to go above 1.71 EC in our parts per million count, because if the electrical conductivity of the suspended particles exceeds that rate, yield losses can occur.

So when we mix in our supplements, additives, and root colonizers (at half-strength only!) we make sure that the PPM doesn’t exceed 1200 in each batch. We had to recalculate the figures given by the Nute Calc, not just by eliminating the suggested quantities of Bloom each week, but also by slightly cutting back on the quantities of the other ingredients.

For pak choi and the herbs we can get away with slightly higher densities of dissolved solids, but lettuce prefers lighter meals. We’re constantly re-evaluating what we’re doing and the recent bolting episode opened our eyes to the importance of protecting our investment.

Growing outdoors, higher fertilizer rates are required during the cold, winter months, but in our environmentally controlled digitally monitored greenhouses we tend to keep the rate of feeding the same year-round. This uniformity of effort is reflected in the uniformly high quality of our produce, much to the delight of our regular customers.

Bolting Lettuce, Chuck and I in Panic Mode

Chuck had to go to Colorado on business, so I stayed behind to man the fort—I mean greenhouses. Now that we have four to look after it’s quite a bit more work, and frankly, it’s much easier when Chuck is around. Then I got a phone call from my ex-wife asking me to come to California to sign some papers.

“Why can’t you fax them to me?” I asked. She explained that because of the confidential nature of the business transaction, the other party specifically asked that they’d be signed in person, in front of a witness.

I spoke to the senior staff-member who has been with us for years, and she assured me that since most of the functions of our four greenhouses are automated, she and the others could look after the operation. She promised that they will harvest and deliver the quota of Butter Lettuce, Pak Choi, and Specialty Lettuce to our clients daily.

The Herb-producing greenhouse hadn’t yet reached the harvest stage, but she would look after that one, as well. In the face of such assurances I felt better and headed to the airport for a quick trip to San Francisco.

After a day spent signing the papers, I had a couple of hours to kill before my flight back, so I went down to the waterfront and decided to have some dinner. I found a small bistro with great food aroma surrounding it, so I went in. At least I thought I entered an eatery. That’s the last thing I remember until I woke up the next day.

A sharp blow to the head knocked me out and my wallet was gone. I was lying on the floor of the entrance to a dilapidated flophouse. Without any money or credit cards it took me a visit to the police station and several frantic calls to the person I left in charge at our greenhouses, in order to have her wire me some money so I could get back. As it was, I could only get a flight the next day.

When I did get back, I found out that they’ve been having some problems. They had an unexpected heat wave and several bright, sunny days in a row, and the shading mechanism on the Specialty Lettuce greenhouse refused to work. No matter how many fans they ran at top speed, the temperature in the greenhouse kept rising and rising.

They tried to cover the greenhouse on the outside with a large, dark green tarp, but the sun kept changing its position and they couldn’t shade the Lettuce properly. They even got some ice cubes and put them in the Nutrient Pond to keep the temperature down.

Intense light for extended periods, coupled with the high temperature (anything above 85º F) will cause lettuce to bolt. Even though we’re very careful to feed our produce with Micro and Grow without the Bloom, the mature Red Sails and Green Ice Lettuce on the Pond bolted.

Bolting lettuce means that it goes into flower production prematurely (i.e. before being harvested), and thus becomes unmarketable. Its taste turns bitter and unappetizing. So not only was my trip disastrous, but I returned to a disaster, as well.

I called Chuck and he took the next flight home. He was mad at me for leaving the greenhouses in someone else’s hands. We both started to panic, but the senior staff member redeemed herself by finding a solution. We lost at most four days worth of produce. At 600 heads per day, that meant we had to replace 2400 heads of Specialty Lettuce. Otherwise we’d be letting our customers down.

She phoned around to other suppliers, some of whom she had worked for in the past, and managed to piece together the order, all 2400 heads. We had it all shipped to our greenhouse, where the produce was repackaged with our logo on it and the trucks arrived to take the first 600 to their destinations.

The other 1800 heads of lettuce are stored in our refrigeration room, standing in ice water. Ice water rejuvenates the cells of the lettuce and allows for a slightly longer storage. Our customers were totally unaware that the quality lettuce we substituted for our own wasn’t exactly harvested that very day.

We had to clean up our Nutrient Pond, thought. Because of the high heat, the humidity increased so I actually discovered signs of Powdery Mildew on some of the bolted lettuce. This insidious fungus will spread very quickly unless it is dealt with right away.

Luckily, Advanced Nutrients has started distributing Protector again, their miracle product which both fights and prevents Powdery Mildew. Not a fungicide, nevertheless it takes care of the problem on edible vegetables much better than using sulphur. Besides, dusting with sulphur leaves a residue and an odor, which is hard to get rid of.

Even though it is not a pesticide, it is not advisable to use Protector beyond the second week of flowering for fruits like tomatoes, where flowering is involved. The ingredients that inhibit the fungus can also change the color of your blooms as well as their aroma.

Chuck and I use it sparingly on Lettuce that is at least 7 days from being harvested. We hadn’t had any discolored leaves or noticeable changes in the aroma of our plants.

The extreme heat also caused some semi-wilting of our younger plants, so we used Advanced Nutrients Revive in order to restore their vitality. This truly remarkable product contains Calcium, Iron and Zinc Chelates, Magnesium, and Nitrogen. It perked up our Lettuce instantly.

We used Revive as a foliar spray, and mixed 5 mL of it per Liter of water. It is absorbed by the leaves of the lettuce and restores not only their robust demeanor, but also imparts a rich, green color, which is desirable in our type of produce.

We also feed our lettuce Mother Earth Blended Super Tea Grow on a regular basis. This 100% organic product enhances our base fertilizers, which are synthetic, with that highly nutritious, organic touch. It contains canola, crab, fish, and shrimp meal, as well as alfalfa extract, citric acid, earthworm castings, and sea kelp.

Sea kelp is rich in natural hormones that promote cell division, root and plant growth, and the distribution of nutrients throughout our Lettuce plants. Enhanced taste and fragrance are also imparted by this product.


Finally, we always add Sensi Cal Mg Mix Grow to our Nutrient Pond, since Lettuce always requires extra Calcium. It is this element that gives Lettuce its crunchy texture. This product is specifically designed for the vegetative growth phase and contains three kinds of Calcium, which are easily absorbable and help our lettuce grow large, healthy, and tasty.