Biodegradable Mulches

“I value my time too much to want to spend it ripping up plastic in the fall,” is Andrew Frankenfield’s reason for trying biodegradable mulches. Andrew is a Penn State Extension educator in Montgomery County, and he is also a farmer. He tried a half acre of biodegradable mulch this year for tomatoes. “So far it looks good, it is starting to degrade along the sides but the weeds are not breaking through,” he told a group of 50 farmers at a field day at Trauger Farms in Kintnersville, PA this month. As we looked at the four biodegradable mulches planted to tomatoes I heard a great discussion of the benefits and disadvantages.
We all know the benefits of plastic mulch. Not only does it keep the weeds down, it warms up the soil giving us earlier (and more) tomatoes, peppers, eggplants and other heat loving veggies. But it costs us. Farmers estimate it costs $25-100 an acre for labor and disposal of plastic mulch.
A possible alternative to black plastic mulch is biodegradable film mulches that look and act much like black plastic, but instead of ripping them up in the fall, you till them into the soil and the microbes degrade the material, leaving you a clean field (hopefully) in the spring.
Good biodegradable mulches are made from starch (corn or wheat). The starch is food for the microbes. They eat it and turn it into CO2 and water. The material will break down fastest when the microbes are most active – when the soil is warm and moist. An important thing about starch based mulches is they become sticky and adhere to the soil as they break down, instead of becoming brittle and blowing around like some of the older technology.
Some of you may have experienced biodegradable mulches in the past and say no way –too hard to lay with the plastic layer – stuck around for ages – too expensive. . . . .Well it may be time to look again. Some of the new mulches are performing well in research trials. One product (Biotelo) had good soil stretch and field application similar to plastic. The soil temperature and yields for muskmelon were similar to plastic according to a study by Dr Rangaragan at Cornell. In a more recent trial from Dr Orzoleck at Penn State in pepper, cantaloupe, eggplant, zucchini all had as good or better yields with biodegradable mulch films (various brands). Even though the film began to degrade before the crop matured, there was no weed growth or competition.
But the question remains – are the biodegradables economical? I sat down with my neighbor to run a few numbers. He figures he uses about 7,000 feet of plastic per acre (1,000 ft rows, 6 ft centers). For the cheapest of the biodegradable mulches I found that is a little less than one 8,000 ft roll at $349/ A for biodegrable mulch. Regular plastic mulch runs him $95 per 4,000 ft roll. At two rolls per acre it costs him $200/ A for plastic mulch. But that does not take into account the cost of ripping up the plastic and disposal. He just pulled up an acre this morning. In two hours for three guys, plus the tractor operator, it cost him about $100 per acre. Disposal in this area is about $50/ Ton. For about 400 lbs/ A of plastic disposal is another $10/ A. Including these extra costs that is $310/ A for plastic mulch plus removal and disposal. That does not include the time and hassle to dispose of it.
I don’t think the final word is in on biodegradable mulches. But it looks like they are worth experimenting with.
Orzolek, M. D. 2007, 208, 2009. Metabolix Field Research; Center for Plasticulture, Penn State University. mdo1@psu.edu
Orzolek M. D. and B. Dye 2008. Paper Mulch Evaluation Study; Dept. of Horticulture, The Pennsylvania State University. mdo1@psu.edu
Sorkin, L. 2006. New biodegradable mulch is cheaper than plastic when removal and disposal costs are also Considered. Cave Moose Farm SARE Project. lauraglenn@hotmail.com

Rangarajan, A. Ingall, B. 2006. Biodegradable Mulch Product Testing. Department of Horticulture Cornell University. ar47@cornell.edu

Spinach Leaf Miner

Spinach leafminer seems to be more prominent than usual this spring in Southeastern Pennsylvania. After receiving a call, I started asking growers and many of them have seen it in fields that are not usually affected. I have seen leafminer damage in Swiss chard, beets and even arugula, in addition to spinach this year.

From a distance, damaged leaves will appear to have blisters – white squiggles on the leaves. When you take a closer look, you may be able to see the legless, yellowish-white larva burrowing between the leaf layers. When the larva is mature, it will cut a hole in the leaf, drop to the ground and pupate. Two to four weeks later it will emerge as an adult fly. The flies are small – 1/4-inch long. Apparently, they are gray with black bristles, but without a hand lens they look like any other small fly to me – perhaps a little slimmer. The adult flies lay clusters of small, white eggs on the leaves.

Usually early spring plantings escape damage. This year the soil temperatures warmed up sooner in places – possibly contributing to earlier than normal problems.

What can you do? Start with cultural controls. Once the leafminer larvae are inside the leaf they are relatively protected from pesticide applications. Crop rotation is important for leafminers. Spinach, beets and Swiss chard (and apparently arugula) are hosts. Make sure you plant in an area that has not seen these crops for two to three years. The spinach leafminer flies overwinter in or near spinach fields and emerge in April and May to lay eggs. Planting early or overwintering spinach can help you escape significant damage, especially if you will be harvesting before mid-May. Deep spring plowing can also reduce the numbers of overwintering fly pupae.

In smaller plantings, they recommend using row cover. The row cover keeps out the egg-laying adults. Install the row cover immediately when you plant, and keep it in place until harvest. One note of caution: If you place row cover over beds that have overwintering leafminers or flies enter under the row cover, you are trapping them inside. The naturally-occurring predators and parasitoids would normally be helping you keep the populations down. Instead, you have created a haven for leafminers and they will multiply!

Unfortunately, if you have significant leafminer problems now, it is hard to go back and do cultural controls. If possible, it is a good idea to pick and destroy leaves with leafmining damage before the larvae emerge and lay eggs for the next generation. On a small scale it is possible to scout for and destroy eggs. For organic growers, Entrust is the only labeled product that has shown any efficacy in research trials. It will penetrate leaves and so it has more activity. Other products, including garlic, may be effective; unfortunately research trials are lacking to back them up. I have also heard of growers using beneficial nematodes. Non-organic growers can use abamectin, cyromazine, dinotefuran, permethrin and
spinosad products.

See the 2010 Production Guide for Organic Spinach at www.nyipm.cornell.edu/organic_guide and Commercial Vegetable Production Recommendations at http://horticulture.psu.edu/node/465 for details.

Are you using more compost or manure than you should?

“Putting on too much compost is expensive and it pollutes.” - Klaas Martens. Organic Grain Farmer. Finger Lakes, New York.

We all know that using organic nutrients such as compost and manure have many benefits. They can increase organic matter, improve soil structure and build a reserve of nutrients in the soil. But the difficulty with using compost and manure is they release nutrients slowly at rates that we cannot always predict. Often the ratios of nitrogen to phosphorus and potassium don’t match what our plants need.

Recently I learned that there can be too much of a good thing. I spoke last week to Klaas Martens an organic grain farmer in the Finger Lakes region of New York. Working with Thomas Bjorkman, a researcher from Cornell, they applied a poultry based compost at different rates in order to determine if they could predict the best compost applications using traditional soil test recommendations. They found that compost applied at rates based on the soil test, did not increase yields or increase organic matter. But, weeds grew better! Where compost was applied at double the recommended rate, weeds were twice as tall (Bjorkman, 2008).

Over application severely impacts the environment. Agriculture account s for 73% of nitrogen and 64% of phosphorus in the Chesapeake Bay. Excess nitrogen easily leaches into ground water and into streams. Phosphorus binds tightly to soil particles that are washed into streams. These nutrients encourage growth of algae and aquatic weeds that use up the oxygen dissolved in the water, making it impossible for fish and other organisms that need this oxygen to survive.
Even the best organic farmers commonly over apply. Researchers surveying organic farms in the Northeast found that vegetable farms that relied on compost often had surplus nutrients, as much as 180-200 lb P and N/ acre – yr in excess (Drinkwater et. al. 2005).

It is easy to apply too much. We often apply at a rate of 1” or 2”s which is easier than calculating how many tons we are applying. Researchers at Penn State did just this, applying 1” or 2” of dairy based compost compared to inorganic fertilizer before peppers. They found that adding just 1” of compost released 441 lbs N/acre compared to the 100 lbs N/acre the peppers needed. This was considering that compost generally only releases 15% of its N per year. Another 2,450 lbs of N/ acre was still tied up in soil organic matter (Sanchez, 2008).

Don’t guess, soil test. Test your compost and soil. If your soil nutrients are too high (over 320 P2O5, 335 K2O, 2505 CaO, 490 MgO lbs/ acre), compost may not be the best choice this year. You will know your soil test is saying you are to high when the bars go into the “exceeds crop needs” section of the table.

Don’t guess, compost test. There is no such thing as the average compost. The average nitrogen content of 126 dairy manure based compost samples analyzed at Penn State was 1.45% nitrogen. But when we looked at three individual dairy manure compost samples from the same farm, the amount of nitrogen applied in 20 ton/ acre of compost ranged from 510, to 415 to 842 lb/ acre. Phosphorus ranged from 88, to 146 to 200.

If your soil test is okay calculate how much N,P,K is available based on your compost test. The compost you apply will be decomposed by bacteria and fungi that live in the soil which release the nutrients slowly over time. Use simple calculations available in Penn State publications “Managing Organic Nutrient Sources” to evaluate how much compost to apply to meet your crop needs. We have also put together a flow chart to help you decide which calculations to do for your farm. Ask for the “Organic Nutrient Sources Decision Making Tree.”