• Numerous pests and non-pests are being found near poor emerging/slow-growing plants.
• Many are attracted by and feeding on dead/decaying plant material.
As pest managers and producers inspect crops that have been “popping” out of the ground, a multitude of insects and other arthropods are being found in the soil. Some are known pests and several are being falsely accused of causing stand reductions. Here are a few of the more common inhabitants found in and around damaged/rotten seed.
Millipedes are very common, usually dark grey or black arthropods (like insects, they belong to the Phylum Arthropoda-means “jointed foot”), having two pairs of legs per body segment. Milli = thousand, pede = feet. They don’t have that many feet, usually under a hundred or so in local species. They become more prevalent as crop/cover residues becomes more abundant. They are often found in large numbers, but are rarely a pest. This is because they typically feed as scavengers, feeding on dead or decaying materials often associated with seedling blights. They are commonly found near any rotting plant material with other arthropod “recyclers”. Several pest managers have reported numerous millipedes in and around corn kernels/sprouts that have been in the ground for two or more weeks. These kernels were probably the victims of pathogens of some kind (bacteria/fungi) and opportunistic millipedes were merely acting as the “clean-up crew” and hollowing out kernels that were in early stages of decay. A healthy and growing corn plant is of no interest to these organisms.
Immature millipede next to rotting corn seedling
Juvenile (“baby”) earthworms (Lumbricids) and potworms (Enchytrids) are closely related and common animals found in soils. They are small, generally colorless/transparent or off-white, and often less than 1/2 inch long. These worms feed on damaged and decaying plant remains, not live tissue. Therefore they are closely associated with the decaying plant parts and surrounding soil and sometimes wrongly accused of damaging seedlings – in fact, they usually arrive after the seed is dead and are attracted by gasses like CO2 that are given off by bacterial rots. In fact, their mouthparts are incapable of causing damage to live tissue – they don’t have “teeth” and instead are specialized to suck up partially-liquefied material. Remember, tkeep an open mind when diagnosing field problems. As one submitter confessed, he was so convinced that it was an insect problem and therefore looked for anything moving when he couldn’t find grubs or wireworms.
Potworms next to damaged soybean seedling
Many other critters, e.g., mites, symphylans, and springtails, have been observed on or around rotting seeds/seedlings. They are small, some fast moving, and certainly unfamiliar to most. They are not causing the poor emergence/growth, but taking advantage of weak and dying plants (including dead weeds and crop debris from previous years) in various stages of decay, as well as the hospitable environment supplied by atypically wet soils. A decaying corn seed is a rich source of nutrients in the mostly-barren environment of newly-planted fields. As a result, many different organisms will arrive to for the feast, the vast majority are not pests.
Two species of springtails u nder high magnification
The majority of corn and soybean acres in the state of Indiana have been planted and are quickly advancing through their growth stages. The time to start scouting fields and identifying weeds for post-emergence herbicide applications is quickly approaching, if not already here for many producers.
At our Palmer amaranth research plots located in Cass County we already have Palmer amaranth plants that have emerged and have quickly reached 2-3 true leaves. For those producers living in the Northwestern quadrant of the state, you need to be on high alert for the presence of this weed in your fields. Even if it was not present in your fields last year, you need to be aware of this weed and able to distinguish it from the other pigweed species. Palmer amaranth is potentially the most aggressive agronomic weed Indiana producers have ever dealt with, and must be managed with an aggressive control program. Seed bank populations will increase quickly in fields where Palmer amaranth is not correctly identified or managed leading to several years of expensive control programs to manage this aggressive weed.
The first key, as eluded to earlier, is the correct identification of palmer amaranth and it’s very close amaranth relatives: common waterhemp, redroot pigweed, and smooth pigweed. A large majority of the populations discovered last fall had been misidentified as waterhemp for a number of years, which allowed the populations to spread quickly to unmanageable levels.
Differentiating a redroot or smooth pigweed from Palmer amaranth is as simple as looking for fine hairs on the stems and leaves. Redroot and smooth pigweed will have obvious fine hairs on the stems and leaf surfaces, whereas Palmer amaranth will be hairless.
Identifying the differences between Palmer amaranth and common waterhemp (both species are hairless) is much more difficult, especially at a young age. At the cotyledon and first true leaf stage it is even difficult for trained weed scientist to differentiate Palmer amaranth from common waterhemp. A few differences that you can note as these plants begin to put on the second and third true leaves are as follows. We have also included a few images for your reference.
•Singular hair in the leaf tip notch: a characteristic of all pigweed (amaranth) species is a notch in the leaf tip. In the plants we have examined from around the state of Indiana it has been consistent that the first, second, and/or third true leaf of Palmer amaranth can have a small singular hair that protrudes from the leaf tip notch. This singular hair often does not occur on all leaves, but is likely to occur on at least one leaf in the early growth stages. We have not observed this singular hair in the leaf tip notches of common waterhemp seedling from the state of Indiana.
•Petiole length of the first true leaves: As noted in our Palmer amaranth biology, identification and management publication (WS-51), one of the main characteristic differences in waterhemp and Palmer amaranth is the length of the petioles. In Palmer amaranth plants the petioles can be as long or longer that the leaf blade itself. In the Palmer publication we included pictures of mature plants, but this characteristic can be observed in two to four true leaf plants as well. As Palmer plants begin to add the second and third nodes the first true leaf will begin to rapidly elongate its petiole to capture sunlight outside of the shadow of the newly emerging leaves above it. The petioles of common waterhemp will consistently stay short, and the leaf blades themselves will be elongated to capture more sunlight. The elongating petioles of Palmer amaranth seedlings will also begin give the seedling the characteristic rosette pattern as you look down at the growing point.
These two characteristics are the most evident differences between Palmer amaranth and common waterhemp at the seedling growth stages. As the plants become larger, all of the characteristics noted in our Palmer amaranth publication (WS-51) will become more noticeable and evident. Although proper identification of seedling plants is necessary in order to make herbicide applications at the 3-6” weed heights that has are recommended for post emergence Palmer amaranth control.
More in-depth identification and management information is contained in our Palmer amaranth publication (WS-51) that is available from the Purdue Education Store <https://mdc.itap.purdue.edu/item.asp?itemID=21061#.UaUcH-ujTq0>.
A photo of Palmer amaranth seedlings taken in Cass County Indiana on May 20, 2013
Producers in the hihglighted counties shold be on high alert for the presene of Palmer amaranth in their corn and soybean fields. The highlighted counties have either had Palmer amaranth reported within that county or a neighboring county.
A redroot pigweed or smooth pigweed seedling with fine hairs present on the stem and leaf surfaces.
A common waterhemp seedling lacking the singular hair in the leaf tip notches. Also note the long linear leaf blades attached to short petioles, especially the first true leaves.
A Palmer amaranth seedling with the singular hair in the leaf tip notch of the second true leaf.
Another Palmer amaranth seedling exhibiting the singular leaf tip notch hair on the second true leaf.
A Palmer amaranth seedling at the three true leaf stage that exhibits the elongated petioles of the first true leaves.
Palmer amaranth seedling with the elongated petioles of the first true leaves.
Palmer amaranth seedling with the elongated petioles of the first true leaves.
VIDEO: Palmer Amaranth Identification
Visit our YouTube video on Palmer amaranth identification at: <http://www.youtube.com/watch?v=wNgRvvnPQJ8> .
Recent submissions to the Purdue University Plant and Pest Diagnostic Laboratory (PPDL) highlight the need for careful consideration of fertilizer rate and source when using pop-up fertilizer.
Long-standing recommendations have suggested an upper limit on the quantity of nitrogen (N) and potassium (as K2O) added as a pop-up fertilizer and the avoidance of certain N fertilizers.
Limits on nutrient quantity in pop-up fertilizer applications are primarily based on the potential for salt injury. When fertilizers dissolve they form ions that compete with the germinating seed and seedling for water. Higher amounts of fertilizer or lower levels of soil moisture increase the concentration of salts in the soil and reduce water availability to the plant.
All fertilizers, even those labeled “low salt”, have the potential to injure germination and seedling establishment when placed with the seed.
Therefore, no more than 5 pounds of N plus K2O per acre are recommended for sandy soils (CEC less than 7) and no more than 8 pounds of N plus K2O are recommended for heavier-textured soils (CEC greater than 7).
Specific N fertilizers, such as urea (including urea-ammonium-nitrate or UAN liquids) and ammonium thiosulfate (ATS), are risky when used as pop-up fertilizers and should be avoided because of their potential to form ammonia and nitrite, which are both toxic to germinating seeds and seedlings.
Fig. 1 Damaged roots and seeds likely from pop-up fertilizer application. More than 14 pounds of N per acre were applied in-furrow, mostly as urea-ammonium nitrate. (Photo courtesy of PPDL).
Root Development in Young Corn – (Bob Nielsen) –
Successful emergence (fast & uniform) does not guarantee successful stand establishment in corn. The next crucial phase is the establishment of a vigorous nodal root system. Success is largely dependent on the initial development of nodal roots from roughly V2 (two leaves with visible leaf collars) to V6.
Corn is a grass and has a fibrous type root system, as compared to soybeans or alfalfa that have tap root systems. Stunting or restriction of the nodal root system during their initial development (e.g., from dry soil, wet soil, cold soil, insect damage, herbicide damage, sidewall compaction, tillage compaction) can easily stunt the entire plant’s development. In fact, when you are attempting to diagnose the cause of stunted corn early in the season, the first place to begin searching for the culprit is below ground.
To better understand rooting development and problems associated with root restrictions, it is important to recognize that root development in corn occurs in two phases. The first phase is the development of the seminal or seed root system. The second phase is the development of the nodal or crown root system.
Corny Trivia: Sometimes you may hear the seminal root system referred to as the primary root system and the nodal root system as the secondary root system. This classification was described by Cannon (1949) and certainly makes chronological sense but always confuses me from the standpoint of importance to the plant.
The Seminal (Seed) Root System
Seminal (seed) roots originate from the scutellar node located within the seed embryo and are composed of the radicle and lateral seminal roots. Even though the seminal roots technically are nodal roots, they are traditionally discussed separately from the nodal roots that develop later from the crown area of the seedling.
The radicle root emerges first from near the tip end of the kernel (Fig. 1) and initially elongate in that direction. The lateral seminal roots emerge later from behind the coleoptile and initially elongate in the opposite direction of the radicle root. However, soon both sets of seminal roots begin to elongate downward in response to gravity (Fig. 3).
Fig. 1. Radicle root and coleoptile of pre-VE seedling.
Fig. 3. Seminal root system of VE seedling, but no evidence yet of nodal root system.
Fig. 5. First set of nodal roots elongating from lower most node of crown area of V1 corn seedling
Fig. 7. Seminal and nodal roots of V2 seedling.
Fig. 8. Root hairs on a V2 corn seedling.
Fig. 12. Delayed emerger with healthy lateral seminal roots but damaged radical root.
Fig. 14. Dead radicle root on a delayed emerger seedling.
Fig. 15. Delayed emerger with healthy lateral seminal roots and damaged, but alive, radicle root.
The next two weeks will see slightly above normal temperatures and normal to above normal rainfall. The best chances for rain will be May 30-June 1 and again June 5-7 over the next 2 weeks.
Most places the next 2 weeks will receive 2-4 inches of rainfall with normal being about 2 inches.
The latest rainfall outlook for the next few weeks is available at: