Fungicides and insecticides are applied to soybean planting seed to control early season diseases and insects.  However, proper disposal of treated soybean seed that are not planted is different from that of untreated seed that are not planted.  Also, disposing of rather than planting expensive soybean seed is an economic negative.

An alternative to disposing of treated soybean seed is storing them for future planting.  This option, of course, is dependent on the maintenance of viability and vigor of the seed during storage so that they can be planted the following season with the same expectation of achieving an acceptable stand as in the year of their purchase.

 PAST RESEARCH FINDINGS

• High temperature and relative humidity in a seed storage environment increase the rate of deterioration of seed;


• Seed that are subjected to fluctuating levels of moisture deteriorate faster than seed that are held in an environment with a constant moisture level; and


• Fungi that are present on stored seed are a major cause of quality losses in those seed, and the extent of fungi-related deterioration is dependent on relative humidity.

 NEW RESEARCH

In a soon-to-be-published Crop Science article, a group of Iowa State University scientists report results from a study that was conducted to determine storage environments that would minimize deterioration of treated soybean seed.

 Study Components

• 24 varieties from MG’s I, II, III, and IV;


• Seed treatments: 1) untreated;  2) treated with a fungicide (ApronMaxx); or 3) treated with a fungicide + insecticide (CruiserMaxx);


• Storage environments: 1) non-climate-controlled warehouse (18 to 82̊ F and 37 to 74% relative humidity);  2) climate-controlled cold storage (51±1̊ F and 60±7% relative humidity); or 3) climate-controlled warm storage (78±1.5̊ F and 31±11% relative humidity).

The standard germination test was used to evaluate seed viability and the accelerated aging test was used to measure seed vigor at study initiation and at 4-month intervals from 4 to 20 months after storage.  Fungi present on seed were identified and counted before storage.

Findings

Initial seed germination ranged from 95 to 99%.  Initial seed vigor ranged from 83% to 97%.

Cold storage.  Over the 20-month course of the study, seed lots maintained their viability at 96%, 95%, and 92% for the fungicide-treated, fungicide + insecticide-treated, and untreated, respectively.  Thus, germination did not significantly decline over the 20 months.

After 12 months of storage, seed vigor of treated seed was >83% compared to 69% for untreated seed.  After 16 months of storage, seed vigor of treated seed was ~70%.

These results indicate that treated seed held in cold storage maintained both viability and vigor for 12 months.  Thus, seed that are treated can be safely held in this environment for the next planting season.

Warm storage.  Viability of both treated and untreated seed was maintained at >90% through 16 months.

After 12 months of storage, seed vigor was 72% for the treated seed and 61% for the untreated seed.

Thus, both viability and vigor of treated seed will be acceptable for planting after being held in a controlled warm storage environment for 12 months.

Warehouse.  After 12 months of storage in the warehouse environment, germination was ~90%, but vigor had declined to <20%.  Treating seed did not affect their ability to maintain either viability or vigor for 12 months when stored in the warehouse environment.

These results indicate that seed that are not planted this season will be unsuitable for next year’s planting if they are stored in the uncontrolled temperature and relative humidity conditions of a warehouse.

 Take-Home Message

Soybean seed that are not planted can be safely held over for the next season’s planting if they are kept in the controlled conditions of either cold or warm storage as defined above.

Viability and vigor of seed that will be held over for next season’s planting will be enhanced during both cold and warm storage if they have been treated with a seed-applied fungicide.

Seed that are left over from the current season’s planting will not maintain adequate viability and vigor for the next season’s planting if they are stored in the uncontrolled conditions of a warehouse.  For Midsouth producers, this is especially so since the temperature and relative humidity conditions likely will be harsher than those in the above Iowa study.

Seed viability alone is not a good measure of seed quality after storage.

Use of the above cold and warm environments for storing planting seed will depend on the value of the soybean seed to be stored.  The above study does not address the economics of storing these seed vs. their purchase cost and/or disposal cost.

Composed by Larry G. Heatherly, Mar. 2013, larryheatherly@bellsouth.net