2015 25.4 Scheduling Vegetables Using Degree Days

New Crop Planning, Planting Model from Oregon State University
Nick Andrews, Len Coop and Heidi Noordijk, OSU Extension, Oregon

Endothermic “warm blooded” organisms like birds and mammals maintain relatively constant body temperatures, so their metabolic reactions and development rates are fairly consistent over time. The body temperatures of ectothermic “cold blooded” organisms (i.e. plants, insects, fungi and bacteria) are close to ambient temperature, so their rates of metabolism and development rates are strongly influenced by the temperature of their environment.

Several other factors like moisture, competition (crop spacing and weed density) and direct pest damage can influence crop development rates, but time and temperature (degree-days) can often predict development of plants more accurately than just time (calendar days). We’ve all seen crops grow quickly when temperatures are about right, and slowly or not at all when it’s too hot or cold.

CROPTIME: degree-day website
Oregon State University (OSU) Extension and the OSU Integrated Plant Protection Center are working with seed companies and local farmers to develop a degree-day scheduling website for vegetable growers. CROPTIME (smallfarms.oregonstate .edu/croptime) will predict harvest dates for vegetable varieties prioritized by collaborating growers and seed companies (see page 4 for a list of crops and number of varieties).

Ed Peachey and Aaron Heinrich at OSU Extension are also developing some weed models that will predict when viable seeds are set. Growers will be able to use this information to reduce weed seed rain in organic rotations. OSU Extension’s Dan Sullivan is explaining how degree-days can improve our understanding of the nitrogen cycle. CROPTIME modelers hope to put at least 50 variety specific models online by late 2016, but some crops may need more research before the models are ready.

Around 1730 René A. F. de Réamur first used mean daily air temperatures to predict plant development. Since then biologists have been improving crop models. The use of sine curves can estimate degree-day accumulation between
a lower threshold (the temperature below which the organism does not develop) and upper threshold (the temperature above which the organism does not develop). Visit this UC Davis site for an in-depth discussion of degree-days concepts.

Using degree-days
Orchardists regularly use degree-days to predict insect pest phenology (i.e. codling moth and filbert worm) and disease risk (i.e. apple scab and fireblight). Some degree-day models have been developed for vegetable crops and pests, but the vast majority of fresh market vegetable growers rely on calendar days to maturity provided in most seed catalogs. Frank Morton, owner of Wild Garden Seed in Philomath, OR, breeds vegetables and sells organic seed. “The normal ‘days to maturity’ varietal information available in most seed catalogs is not useful to farmers, except in a vague relative sense,” says Frank. “If seed breeders and catalogs could provide a degree-day index for their vegetable varieties, farmers would be able to more accurately model their crop delivery schedules in years of unusual weather patterns or extremes.”

David Brown from Mustard Seed Farms in St. Paul, OR, is perhaps the only fresh market vegetable grower in Oregon who already uses degree-days to schedule crops. He has developed his own degree-day models for broccoli and other crops. “I have used degree days for over 20 years to schedule successive plantings of vegetables… more information based on some research would be helpful in refining my schedules and maybe even using the information for more crops.” OSU Extension’s goal is to make vegetable degree-day models accessible to more vegetable growers.

In the spring of 2016, producers will be able to use the first CROPTIME models to schedule plantings and predict harvest dates to plan a consistent supply. Up to four planting dates can be entered at a time. There is a new Google maps interface to help select the best nearby weather station (see map display, left). Bob Egger from the Pumpkin Patch on Sauvie Island, OR, explained how a steady flow of crops like cabbage benefits his farm. “When we have a couple weeks of wet weather in spring we could use CROPTIME to choose varieties we might not be familiar with but would help keep our production up. The big buyers don’t waste time with you if you don’t have the right product available at the right time.”

During the season producers can run the models again to access up-to-date harvest predictions. The CROPTIME site uses actual weather data up to the day before a model is run, then five-day forecasts followed by 30-year average temperatures more than five days in the future. Tanya Murray, previously with Sauvie Island Organics near Portland, Oregon, planned each week’s CSA share carefully. “The dramatically different weather we have had this spring and last makes it hard to know what to expect. CROPTIME will help our farm use degree-days to predict maturity.” OSU Integrated Plant Protection Center’s Len Coop is improving the accuracy of long term forecasts by converting the output of NOAA weather models to degree-days.

Arcadia broccoli reportedly takes 63 to 70 days to mature depending on the seed catalog referenced. The preliminary CROPTIME model predicts 74 to 110 days between transplant and maturity in the Pacific Northwest. Days to maturity vary with planting time and year (Figure 1, right). Early spring planted Arcadia broccoli takes 20 days longer or more to mature than mid-summer plantings. Development also progresses more slowly in cooler years (2011-2012) than warmer years (2013- 2015). Crops planted one month apart matured 14-30 days apart (not shown). These models are developed in irrigated Willamette Valley fields. In some regions and cropping systems, environmental factors not well tested here may be more important (i.e. soil moisture, day-length or upper thresholds).

Developing new models
The degree-days models will continue to be refined with the intent to develop new models for winter vegetables and possibly cover crops. Since vegetable varieties change regularly, OSU Small Farms would like to work with others to collect field data and develop models. Please contact them if you are interested. A Vegetable Growth Stage Guide and standard protocols to improve consistency of field observations are also being developed.

CROPTIME includes cool season crops like cabbage and spinach, and warm season crops like peppers and winter squash. Cool season crops have cooler lower and upper thresholds (i.e. 40°F and 70°F for broccoli). Warm season crops have warmer thresholds (i.e. 52°F lower threshold for sweet pepper); it normally doesn’t get hot enough in the Willamette Valley to identify their upper thresholds.

Models require at least eight to 10 data sets (a data set comprises crop development observations at one location or planting date) for each crop to verify threshold temperatures in the literature. Then four to five data sets can be used to estimate the number of degree-days to maturity for each subsequent variety. So far preliminary thresholds have been identified for broccoli, sweet pepper, cucumber, winter squash and sweet corn. 2015 data will be incorporated to finalize the models.

Growing methods included organic, conventional, black plastic, bare ground, direct seeded and transplanted crops. Based on the findings so far, separate models may be needed for some of these practices. In the future the plan is to be able to adjust models to account for the warming effect of black plastic mulch.

Vegetable degree-day models may be a more accurate method than calendar days for scheduling crops. Producers and buyers using CROPTIME may be able improve the consistency of supply, and plan harvest crews and marketing activities more accurately. The weed models may help reduce weed seed rain in crop rotations, and the nitrogen information will add to our understanding of nitrogen cycling in organically managed soils.

Nick and Heidi will present CROPTIME at the Tilth Producers of Washington Conference in Spokane (November 13- 15), and at the OSU Small Farms Conference in Corvallis (February 20, 2016, smallfarms.oregonstate.edu/sfc). OSU Small Farms team is also developing small-group hands-on workshops to teach people how to use CROPTIME.

Nick Andrews is a senior instructor at OSU Extension. He is a member of OSU’s Small Farms Program, and the OSU Center for Small Farms & Community Food Systems. He serves Multnomah, Washington and Clacka¬mas counties and specializes in ecological horticulture. His program focuses on ecological vegetable production and beginning farmer training. nick. andrews@oregonstate.edu; 503-913-9410. Contact Nick for more informa¬tion about CROPTIME.

Len Coop is an entomologist and associate director at the Integrated Plant Protection Center of OSU. He has been working to build weather-driven models for IPM for over 25 years. For the past 20 years Len has been building a website to deliver these models to provide agricultural and IPM decision support for Oregon and other parts of the US. coopl@science.oregonstate.edu, 541-737-5523.

Heidi Noordijk is Educational Program Assistant at OSU Extension. She works closely with Nick and is a member of OSU’s Small Farms Program and the OSU Center for Small Farms & Community Food Systems. She serves Multnomah, Washington and Clackamas counties. heidi.noordijk@ oregonstate.edu, 971-801-0392.

CROPTIME is funded by WSARE Research & Education award number SW12-037 with additional funding from Clackamas Extension Innovation Fund.

Tags: CROPTIME, degree days, scheduling, Vegetable