Irrigation recommendations for fruit crops during drought
While berry growers use irrigation throughout every growing season, irrigation use is less universal in apples and grapes in the upper Midwest. For example, most Minnesota grape growers lack irrigation systems because they are so rarely needed, while others with drip tape report having never turned it on. Irrigation is very important for apples and can be helpful for cold climate grapes in extremely dry years and for newly planted vines.
Grapes
Water availability impacts grapevine vegetative growth, fruit composition, and potentially fruit set and winter hardiness. Symptoms include slow shoot growth, dried tendrils, drooping leaves, and yellowed or dried leaves.
During extended dry periods, the irrigation recommendations depend on the age of the vines. For new vines, a simple guideline is to irrigate 1 inch every 7-10 days. Mature vines require less frequent irrigation due to their more extensive root systems – irrigation 1 inch every 2-3 weeks. The recommendation is the same whether the grower is using an irrigation system or watering tank.
Apples
These past two months have been unusually dry and have resulted in pressing needs for irrigation in high density apple orchards. Lucky for us we have a great tool to estimate water needs with the Cornell apple irrigation model available at the NEWA website.
The Cornell apple irrigation model uses weather data to estimate the amount of water apple trees use daily. The model takes in consideration the age of the tree and the phenological stage (how much of the canopy has developed) to calculate the daily amount of water used. The model also incorporates how much water has entered the system through rainfall to calculate the total amount needed. In addition to rainfall, the volume of water stored in the soil must be considered when calculating irrigation needed. Different soil types have different available water capacities. Sandy soils will have ~30,000 gal/acre of available water; while loam and clay soil will have ~80,000 gal/acre and 110,000 gal/acre, respectively. If we consider that a mature tall spindle orchard will consume 4,000-5,000 gal/day, it means that a sandy, loam, and clay soil will have 7, 20, and 27 days of water supply, respectively. However, as water availability decreases, it is harder and harder for trees to use the water left in the soil, and the general recommendation is to start irrigating when 5,000 to 10,000 gal/acre has been used.
In 2021, rainfall has been insufficient in most of Wisconsin (between 2.5 to 4.5 inches of rain since May 1st). The data from Madison (Table 1), shows that the cumulative water balance fell below 10,000 gal/acre in mid-May for a couple of days until we got some rainfall, but has been under 10,000 gal/acre since June 1st and no rain is forecasted in the next 5 days (the model only allows 5 days of forecasting). Based on the recommendation to irrigate when cumulative water balance reaches 10,000 gal/acre, growers should have began irrigating by May 1st.
Table 1. Daily and cumulative mature tall Spindle apple orchard water use at Verona, WI for the last 30 days.
Date
Tree Water use (gallons/acre)
Rainfall (gallons/acre)
Daily Water Balance (gallons/acre)
Cumulative Water Balance (gallons/acre)
11-May
1337
0
-1337
-4940
12-May
2293
0
-2293
-7233
13-May
2073
0
-2073
-9307
14-May
2101
0
-2101
-11407
15-May
439
380
-59
-11466
16-May
1994
190
-1804
-3963
17-May
1921
0
-1921
-5885
18-May
884
5702
4818
-1066
19-May
668
2851
2183
0
20-May
1477
0
-1477
-1477
21-May
766
3611
2845
0
22-May
2315
190
-2125
-2125
23-May
1472
760
-712
-2837
24-May
2150
0
-2150
-4987
25-May
1653
0
-1653
-6640
26-May
3075
0
-3075
-9715
27-May
297
13305
13009
0
28-May
276
3802
3525
0
29-May
2229
0
-2229
-2229
30-May
2647
0
-2647
-4876
31-May
2597
0
-2597
-7473
1-Jun
3429
0
-3429
-10902
2-Jun
4250
0
-4250
-15152
3-Jun
4457
0
-4457
-19609
4-Jun
4386
7983
3598
-16012
5-Jun
4397
0
-4397
-20409
6-Jun
3912
0
-3912
-24321
7-Jun
2779
0
-2779
-27100
8-Jun
4595
0
-4595
-31695
9-Jun
4234
0
-4234
-35929
10-Jun
4787
0
-4787
-40716
11-Jun
4544
0.05
-3594
-29157
12-Jun
3650
0
-3650
-32807
13-Jun
4460
0
-4460
-37267
14-Jun
4408
0
-4408
-41674
15-Jun
3938
0
-3938
-45613
Resources for Managing Fruit Crops During Drought
The National Drought Mitigation Center has released a variety of resources for specialty crop growers to deal with drought. Find a full list of these resources here.
This includes a set of production calendars designed to help fruit growers decide when and how to irrigate during dry years. One helpful feature of the calendars is that they relate each fruit phenological stage to the drought concerns during that time.
Quick links:
Perennial fruits drought monitoring resources fact sheet
The fact sheets also discuss how to use tools like soil moisture maps, soil temperature maps, the US Drought Monitor, and the evaporative stress index (ESI).
This is a project of the National Drought Mitigation Center and the University of Wisconsin, with the U.S. Department of Agriculture Midwest Climate Hub and the National Integrated Drought Information System.
– Annie Klodd and Amaya Atucha, University of Wisconsin